A truly free SIP trunk covers the account, never the outbound minutes. What’s actually free is a $0-monthly pay-per-use account, a limited-time trial, or in-network calling. No carrier terminates outbound PSTN calls at volume for free, because every call to the public network costs the carrier per-minute interconnection fees.
An account that costs $0 a month is easy to find. A trunk that delivers real outbound calls to the phone network for $0 is not. The gap between those two sentences is this entire market.
SIPNEX is an FCC-licensed carrier that sells SIP trunking — bias disclosed. Here is the honest map: what free SIP trunking includes, what it’s good for, and where the free-adjacent offers quietly cost you.
What a free SIP trunk actually includes
“Free SIP trunk” is marketed in four distinct shapes. Verified examples, all checked August 2026:
| What’s marketed as “free” | Verified example | What costs $0 | What you still pay for |
|---|---|---|---|
| $0-monthly pay-per-use account | Callcentric Pay Per Call / IP Freedom | The account, voicemail, in-network calls | Per-minute PSTN rates; the phone number |
| Free cloud PBX layer | Zadarma free PBX | PBX features: IVR, transfer, recording | The calling itself; paid plans from $4/user/mo |
| Time-limited trial | Kixie 7-day trial; JustGOcloud 30-day promo | Everything, briefly | Full rates when the clock runs out |
| Open-source software | VICIdial, Asterisk | The software license, every feature | Servers, carrier trunks, every minute |
The cleanest version of free is the $0-monthly account. As of August 2026, Callcentric’s plans page lists its IP Freedom outbound plan at $0.00/month. It includes unlimited calling to other Callcentric customers and to other VoIP networks. A Pay Per Call plan is also $0.00/month, billed at per-minute rates. Voicemail is free. Note what’s missing: a phone number. Incoming numbers are paid — a “Dollar Unlimited” DID from $1.00/month (residential only, select US states), or a pay-per-minute DID at $1.95/month plus $0.015/min.
Zadarma inverts the model: the free layer is the PBX, not the trunk. As of August 2026 it advertises a free cloud PBX — IVR, call transfer, call recording, voicemail — plus a free CRM. Paid PBX plans start at $4/user/month. Its homepage doesn’t spell out the free tier’s caps or top-up conditions, so read the tariff pages before building on it. Either way, the calls themselves remain metered service.
The third shape is the trial. Kixie runs a 7-day free trial on its per-seat dialer plans. GOautodial’s hosted JustGOcloud advertises a 30-day promo: the first month free for up to 10 agents. Trials are genuinely free — but they’re evaluation windows, not a phone-bill strategy.
The fourth shape confuses the most buyers: open-source software. VICIdial and Asterisk cost nothing to license — that $0 is real and permanent — but software is not carriage. It’s the one version of “free” that holds up, covered below.
Across the providers we checked, none was verified as advertising a permanently free, full SIP trunk with an included phone number. That’s a survey, not proof about every provider on earth. But the pattern is consistent enough to be your planning assumption.
Why outbound calling is never free
Two definitions make the economics plain. In SIP trunking, origination is the PSTN delivering inbound calls to your systems. Termination is your systems placing outbound calls to the PSTN. Termination costs your provider money on every call: it pays per-minute interconnection fees to downstream carriers to complete your traffic.
That’s why free offers cluster where they do. Free in-network calling is affordable — the traffic never leaves the provider’s switch. A trial is marketing spend. Paying interconnection on your outbound volume forever while charging nothing is neither. Any “unlimited free outbound” pitch is capped, in-network only, temporary — or recovering the cost somewhere you can’t see. Paid “unlimited” plans run on the same fair-use logic; the math is in our unlimited SIP trunk guide.
Free services vs paid SIP trunking services
The free services above and paid SIP trunking services differ on more than price. Put them side by side and the gap is mostly about what you can enforce.
| Line item | Free tier | What to demand from paid SIP trunking services |
|---|---|---|
| The account | $0 per month | A price per month, per channel, or per minute — in writing |
| Outbound PSTN calls | Metered, or in-network only | A published per-minute rate and a stated billing increment |
| Phone number | Often a separate charge — Callcentric prices DIDs from $1.00/month | Numbers itemized per month, with porting terms |
| Concurrent calls | Confirm the cap before you test anything that dials | Capacity sized to your busy hour, per channel or unlimited |
| Service level agreement | Nothing to enforce on a $0-monthly tier | Availability terms, support response times, service credits |
| Caller-ID signing | Whatever the provider applies by default | Who signs STIR/SHAKEN, and at which attestation level |
Run every one of your SIP trunk options through the right-hand column. A free tier fails most rows by design. That is fine for a lab. It is the wrong shape for a production floor.
Concurrent calls: the cap that ends the free tier
In SIP, the trunk is the account. A channel is one live call on it. Concurrent calls are the channels in use at the same moment. A lab needs one or two. A small office needs a handful. A dialer floor needs far more, because a predictive dialer places more calls than it has agents to take them.
Ask three questions before you test on a free tier. How many concurrent calls does the account allow? Is the cap per account or per registration? What happens to the call that crosses it — a busy tone, a SIP 503, or a silent drop? The same questions belong on the list for any paid provider; they are in our seven-question SIP trunk provider checklist.
Bandwidth is rarely the constraint. G.711 needs roughly 85 kbps per direction per call, so 20 concurrent calls fit inside 2 Mbps. On a lab connection the account cap, not the internet line, is the limit to ask about. When the traffic is real, size channels with our SIP trunk sizing guide.
Quality of service (QoS) on a free trunk
Quality of service (QoS) is two jobs, and a free tier touches only one of them. On your own network, QoS means marking voice packets so your router sends them first. Voice media should carry DSCP 46 — Expedited Forwarding, defined in RFC 3246. Signaling is commonly marked CS3. Most IP phones already mark by default; the step people skip is setting the router and switches to honor the marking.
ISPs generally do not honor DSCP across the public internet, so QoS protects the links you control: your LAN and your own uplink queue. All of that is free on any trunk. The setup is in our packet loss fix guide.
The second job is the carrier’s route. Latency, jitter, and loss between your provider and the far-end carrier depend on whose network they buy from. A free tier gives you no say in that path and no one to call when it degrades. Measure it anyway: one-way latency under 150 ms is acceptable, and under 80 ms is good. The full set of targets is in our jitter, latency and MOS guide.
Service level agreement: the line no free tier signs
A service level agreement is a contract. It states the availability the provider promises, how fast support responds, and what you get back when they miss — usually service credits. Credits are applied against an invoice. A $0-monthly account has no recurring charge to credit against, and no availability promise to enforce. That is not a knock on free tiers. It is what free means. Treat them as best-effort.
When you move to a paid trunk, read the SLA before the rate card. Look for the availability figure, how downtime is measured, the credit schedule, and the exclusions. When a vendor calls its service enterprise grade, ask for the SLA document behind the phrase. Enterprise-grade is a claim; the agreement is the proof.
Unified communications suites vs a bare trunk
Some people searching for a free SIP trunk actually want a phone system. A unified communications suite — RingCentral, Vonage, 8x8 and their peers — bundles the phone system, the numbers, and the calling into one per-seat subscription. The trunk is priced into the seat, so nothing in it is free. Those plans also ban auto dialing outright; our guide to SIP providers that allow auto dialers has the policy map.
Pick the shape by what you run. If you want an office phone system with nothing to host, compare the paths in our hosted PBX vs SIP trunking guide. If you run your own PBX or dialer and need carriage under it, a trunk is the right shape — free for the lab, paid for production.
What free SIP trunking is genuinely good for
Free tiers earn their keep in the lab. Use them to validate a PBX config, test a softphone, learn SIP signaling, or prove your firewall and NAT behave before any money moves. The settings you validate on a free tier — codecs, registration, DTMF — move unchanged to a production carrier. That is the sequence our Asterisk SIP trunk configuration guide recommends.
The line to hold: free tiers validate configuration, not capacity. Answer rates, caller-ID reputation, concurrency, and route quality only reveal themselves under production traffic.
The free-adjacent traps
Three offers sit close enough to “free” to deserve a closer read.
Trials that want a card. A trial with a credit card attached is a subscription with a delay. Before testing, check what happens the day the trial ends. Auto-conversion pricing is where the real rate hides.
“Free minutes” bundles. Bundled minutes aren’t free. They’re priced into whatever the bundle is attached to — a seat license, a platform fee, a higher per-minute rate after the allowance. Compare the all-in cost per minute, not the headline.
Grey-market resellers. The most expensive “free” is the unauthorized reseller pushing cut-rate, multi-hop routes. Cheap multi-carrier routing has measurable symptoms. Bandwidth’s glossary notes that post-dial delay is more common on wholesale least-cost routing products. Each carrier in the chain takes a few seconds to confirm it can complete the call. Caller-ID trust degrades across those chains too — the i3Forum’s Restore Trust initiative exists for exactly that reason. The honest breakdown of direct versus multi-hop routing is in our VoIP routes guide.
What legitimately cheap looks like
Since free outbound doesn’t exist, the real question is what fair looks like. Three markers:
Published per-minute rates. Printed prices are prices you can hold a provider to. SIPNEX publishes its rates; many providers quote only through sales calls.
Dialer-friendly billing increments. The big CPaaS platforms — Twilio and Telnyx among them — bill voice at 60/60. Every call rounds up to a full minute. SIPNEX bills dialer traffic 12/6: a 12-second minimum, then 6-second increments. A 45-second call bills as 48 seconds instead of 60. On short-call outbound traffic, the increment moves the bill more than the rate does.
Transparent number and feature pricing. DIDs, e911, and channel policy priced in the open, not discovered on the first invoice. The full teardown of what SIP trunking should cost — rates, increments, fees, and the comparison math — is in our SIP trunk pricing guide.
Free auto dialer software: the honest shortlist
Many “free SIP trunk” searches are really about free auto dialer software. Three names come up. Two are worth your time.
| Software | License | Status (August 2026) | What the $0 covers |
|---|---|---|---|
| VICIdial | AGPL | Developed and maintained by the VICIdial Group; deployed in 100+ countries | Predictive dialer, inbound ACD, recording — the whole suite |
| GoAutoDial Community Edition | AGPL | Maintained; built on the VICIdial engine and Asterisk | The suite, self-installed from its own ISO |
| OSDial | AGPL | Last release March 2014 — treat as unmaintained | A decade-old VICIdial fork; skip it |
None of the three ships with a carrier. The software places zero calls until you connect a SIP trunk. Start with the official VICIdial download. If the interface is your complaint, our VICIdial alternatives guide weighs GoAutoDial against the rest. The GoAutoDial trunk wiring is in our GoAutoDial SIP trunk guide.
The real free stack: VICIdial plus paid carriage
The answer to the free-dialer question has existed for two decades: VICIdial is the free dialer. Open-source under the AGPL, no license cost, full predictive dialing, inbound ACD, and recording included — self-installed on servers you control.
That’s the version of “free” that holds up in production: free software plus paid carriage. The software line genuinely is $0 forever. The carrier line is metered, negotiable, and honest. Free software plus “free” carriage isn’t a stack — it’s a trial. What the $0 license actually costs to run — servers, expertise, telecom, compliance — is mapped line by line in the VICIdial pricing breakdown. The trunk wiring lives in the VICIdial trunk configuration guide.
Frequently asked questions
Does a completely free SIP trunk with a phone number exist?
Not from any provider we could verify as of August 2026. The verified free offerings are narrower. Callcentric offers $0-monthly pay-per-use accounts and free in-network calling. Zadarma offers a free cloud-PBX layer with metered calling. Kixie (7 days) and JustGOcloud (a 30-day promo) offer time-limited trials. In every case the phone number, the outbound PSTN minutes, or both stay paid. Treat any permanently-free-with-number claim as fine print to read, not a plan to build on.
Why is there no free SIP trunk for outbound calls?
Because termination costs the provider money on every call. When your trunk sends a call to the PSTN, your provider pays downstream carriers per-minute interconnection fees to complete it. In-network calls can be free — they never leave the provider’s switch — and trials can be subsidized briefly. But nobody can absorb interconnection fees on real outbound volume forever while charging nothing. Free outbound at scale isn’t sustainable pricing. It’s a red flag about where the money actually comes from.
What is a free SIP trunk actually good for?
Lab work — and it’s genuinely good at it. A $0 account lets you validate PBX configuration, codecs, registration, DTMF, and firewall behavior before spending anything. Those settings transfer unchanged to a production carrier. What a free tier cannot tell you is how your traffic performs at volume. Answer rates, caller-ID reputation, concurrency, and route quality only show up on production trunks. Validate config for free; buy capacity when it’s time to dial.
What should replace a free SIP trunk in production?
A carrier with published per-minute rates, billing increments that fit your traffic, and its own regulatory standing. For dialer traffic, increments matter most: 60/60 rounding punishes short calls, while 12/6 billing charges a 45-second call as 48 seconds. Direct carriers can also sign their own STIR/SHAKEN attestation instead of inheriting a reseller’s. SIPNEX is an FCC-licensed carrier with published rates, 12/6 dialer billing, and A-level attestation signed under our own certificate. That is the checklist we’d apply to anyone, applied to us.
How many concurrent calls does a free SIP trunk allow?
Only what the provider’s terms allow — look for the cap in the terms of service, not the headline plan. A lab needs one or two channels. A small office needs a handful. A predictive dialer needs many more, because it keeps more calls in flight than it has agents. Confirm the cap, and what happens when a call crosses it, before you point any dialer at a free tier. Size production channels against your busy hour, not the free tier’s ceiling.
Does a free SIP trunk come with a service level agreement?
Expect none. A service level agreement pays out as service credits against your invoice, and a $0-monthly account has no recurring charge to credit against. Treat every free tier as best-effort, with no promised availability and no promised support response. When you move to a paid trunk, read the SLA before the rate card: the availability figure, how downtime is measured, the credit schedule, and the exclusions.
Is free auto dialer software the same as a free SIP trunk?
No. Free auto dialer software is the application — VICIdial and GoAutoDial are AGPL open source with no license fee. A SIP trunk is the carriage that connects the dialer to the phone network, and outbound minutes on it are always metered. The two get confused because both are searched with the word “free”. The software can be $0 forever; the trunk can be $0 only for the lab, in-network calls, or a trial.
Does quality of service (QoS) help on a free SIP trunk?
On your side of the connection, yes — QoS is free to set up on any trunk. Mark voice media DSCP 46 (Expedited Forwarding) and set your router and switches to honor it, so voice packets leave before bulk traffic. What QoS cannot fix is the carrier’s route: latency, jitter, and loss beyond your uplink are set by whose network the provider buys from. A free tier gives you no say in that path, and nobody to call when it degrades.
Free tiers are for the lab. When the traffic is real, the honest math is published rates and dialer-grade increments — see our pricing or call (833) 665-2220.
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