Unlimited SIP trunks are real only for conversational office calling. Every major unlimited or flat-rate plan we reviewed carries a fair-use policy, and every policy restricts autodialing, predictive dialing, or call-center use. For steady PBX traffic, per-channel unlimited pricing is legitimate and often cheaper; for dialer traffic, no plan is unlimited — metered billing is the honest model.
If you searched “unlimited SIP trunk provider” for an office phone system, the plans work as advertised. If you searched it for a dialer, the fine print is written specifically to exclude you — and this post shows you exactly where.
SIPNEX is an FCC-licensed carrier that bills dialer traffic metered, so we have a position in this fight — bias disclosed. The teardown below quotes the vendors’ own published policies, not our opinion of them.
What “unlimited SIP trunking” actually means
An unlimited or flat rate SIP trunk sells you a channel — one concurrent call path — for a fixed monthly fee, with no per-minute charge on domestic calls. The economics only work for the provider because a typical office channel sits idle most of the day. The plan is priced against conversational usage patterns: human beings, dialing occasionally, talking for a few minutes.
That assumption is not left implicit. It is written into the terms as a fair-use or acceptable-use clause, and the clauses are remarkably consistent across the industry. “Unlimited” means unlimited for the traffic profile the provider expected — and the expected profile is never a dialer.
The fine print, provider by provider
Here is what the unlimited and flat-rate policies actually say, from the vendors’ own published documents:
- Telnyx — the acceptable use policy prohibits, “with respect to any unlimited calling package, in addition to any other of the prohibited uses, auto-dialing, continuous or extensive call forwarding, continuous connectivity, fax broadcast/blasting, telemarketing, predictive dialing, or any other use or activity that is inconsistent with normal small to medium sized business usage.”
- Vonage — the reasonable use policy states the service “may not be used for auto-dialing, continuous or extensive call forwarding, excessive conferencing, inbound/outbound centralized or distributed call center activity, telemarketing,” and that unlimited small-business plans “are intended solely for normal commercial use by small businesses and home offices.”
- 8x8 — the business terms restrict unlimited PSTN plans to “reasonable business use of Customer only,” explicitly excluding “any autodialing… telemarketing… call center operations,” and reserve the right to “immediately terminate or modify” service for misuse.
- RingCentral — the acceptable use policy prohibits customers to “perform auto-dialing or ‘predictive dialing’” and states the RingEX services “are intended for regular business use between individuals and not for high-volume commercial messaging or call center calling.”
- voip.ms — any telemarketing-type use, “including but not limited to automated dialers, call centers, collection agencies, dialer traffic, and polls,” requires pre-authorization, and unauthorized use may be suspended “without prior notice.” Short-duration calls — under 6 seconds of signal — need separate pre-authorization.
Five providers, five different documents, the same underlying position: the unlimited price assumes you are not a dialer. This is not a loophole you can quietly slip through. Suspension clauses attach to exactly this behavior, and our guide to what to do when a dialer account gets suspended exists because providers enforce them.
Telnyx’s general policy goes further than the unlimited clause: it lists autodialing and predictive dialing among improper uses of the services overall, and separately flags low answer-seizure rates and excess calls-per-second as violations. Dialer traffic there is a policy question well beyond plan choice — the full landscape is mapped in our review of SIP providers that allow autodialers.
The math: flat rate vs metered for dialer traffic
Set policy aside for a moment and run the numbers as if an unlimited SIP trunk provider would take your dialer traffic. Industry pricing guides put flat per-channel plans in the rough range of $15–$25 per channel per month, varying by provider, term, and bundle. A predictive dialer needs several channels per agent to keep pacing ahead of answers — commonly around three or four — so a 20-agent floor is shopping for 60–80 channels. At the middle of that advertised range, the flat-rate bill lands in the $1,200–$1,600 per month neighborhood before the first minute is placed.
Metered billing prices the same floor on what it actually uses. Dialer traffic is dominated by short calls — voicemail drops, quick disqualifications, wrong numbers — and short calls are where billing increments decide everything. On Twilio’s standard pay-as-you-go pricing, voice bills in 60-second increments: partial minutes round up, so a 1:20 call bills as two full minutes, and the policy applies to Elastic SIP Trunking. A 25-second dialer call bills as a full minute — 2.4× the airtime you used.
SIPNEX bills dialer traffic 12/6: a 12-second minimum, then 6-second increments. The same 25-second call bills as 30 seconds — half of what 60/60 rounding charges for it. Multiply that gap across tens of thousands of monthly dials and the increment, not the headline rate, becomes the largest lever in the bill. Generic rate-by-rate shopping is a separate exercise — our SIP trunk pricing comparison covers it — and we deliberately don’t publish a termination rate table here. The honest version of that conversation is pricing your actual CDRs, not a table’s best-case row.
When unlimited genuinely wins
Flat-rate channels are the right buy for steady conversational traffic. An office PBX with predictable human calling — sales calls dialed by hand, support lines, professional services — gets budget certainty, and heavy talkers on long calls can genuinely come out ahead of metered billing. If that describes your traffic, an unlimited SIP trunk is a fine product; start with what SIP trunking is and how it connects to a hosted PBX, and buy with confidence.
The test is simple: if every call on your trunk is a human being who dialed or answered on purpose, you are the customer these plans were priced for. The fair-use clauses will never apply to you, and the flat fee is real.
When metered wins
Metered billing wins whenever traffic is bursty, short, or automated — which is to say, whenever a dialer is involved.
- Short calls. At a 25–35 second average, 60/60 rounding roughly doubles billed time. Metered carriers with dialer-grade increments — SIPNEX bills 12/6 — charge close to actual airtime.
- Burst capacity. A dialer’s channel demand spikes at campaign start and collapses between lists. Flat-rate channels bill for the peak all month; metered trunking bills for usage.
- Policy survival. This is the one that actually ends accounts. Metered, dialer-aware carriers underwrite your traffic profile up front instead of terminating you for it later.
There is no unlimited plan that beats metered billing on traffic the unlimited plan prohibits. That sentence is the entire buying guide for call centers, and platform-specific carrier choice — like the best SIP trunk for VICIdial — starts from it.
How many channels do you actually need?
Whichever model you land on, size the trunk before pricing it. Conversational offices size to peak concurrent calls — usually a small fraction of headcount; dialers invert that math, needing multiple channels per agent to feed pacing. The sizing math — concurrency, Erlang assumptions, dialer ratios — is worked through in our guide to how many SIP trunks you need. Get the channel count right first; it changes which pricing model wins.
Frequently asked questions
Is any SIP trunk truly unlimited?
For conversational business calling, effectively yes — within fair use. Every unlimited plan carries an acceptable-use policy assuming normal human calling patterns; stay inside that profile and the flat monthly fee is genuinely all you pay. Step outside it — autodialing, call-center volume, continuous connectivity — and the same policy authorizes suspension or forced plan changes. “Unlimited” describes minutes, not permitted uses.
Do unlimited SIP trunk plans allow autodialers?
No — every unlimited policy we reviewed restricts autodialing. Telnyx’s unlimited-package clause bans auto-dialing and predictive dialing; Vonage, 8x8, and RingCentral publish equivalent prohibitions; voip.ms requires pre-authorization for any dialer traffic. Dialer operations need a carrier that accepts the traffic profile explicitly and prices it metered, not a flat-rate plan whose terms exclude them.
Is an unlimited SIP trunk cheaper than metered billing?
For long, steady conversational calls, often yes; for short or bursty traffic, almost never. A flat channel fee beats metered billing when the channel carries heavy talk time all month. Dialer traffic inverts the math: short calls bill near actual airtime on dialer-grade increments like 12/6, while flat-rate plans charge for peak channel count around the clock — and prohibit the traffic anyway.
What happens if I run dialer traffic on an unlimited plan?
Expect enforcement, not a warning shot. voip.ms reserves the right to suspend unauthorized telemarketing traffic without prior notice, including its DID numbers; 8x8 reserves immediate termination or modification for unlimited-plan misuse; Vonage’s policy mandates plan transfer, suspension, or termination for unusual calling patterns. A mid-campaign cutoff costs far more than metered rates ever would — plan a carrier strategy with failover instead.
If your traffic is conversational, buy the flat rate with our blessing. If it’s dialer traffic, price it honestly: send us your actual CDRs and we’ll quote against them — 12/6 billing, A-level attestation from our own STIR/SHAKEN certificate, and a carrier that already knows what your traffic looks like. (833) 665-2220.
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