The best SIP trunk for VICIdial is a carrier that permits dialer traffic in writing, sustains your calls-per-second and channel load without discretionary surcharges, bills short calls in short increments (12/6, not 60/60), signs outbound calls with A-level attestation, and clears short-duration traffic in its terms. Most consumer and CPaaS trunks fail at least two of those five tests.
If you’re asking this question, you’ve probably noticed nobody answers it in public. Run any VICIdial SIP provider through the seven criteria below and the field narrows itself.
Why the forum won’t answer it
Ask “which SIP trunk should I use?” on the official VICIdial forum and watch what happens: vendor names don’t get posted, and the thread ends in “test a few and see.” The moderation is rational — a recommendation thread with vendor posts left standing becomes an ad board — but the result is that the most consequential purchasing decision in a VICIdial deployment has stayed unanswerable there for over a decade.
We’re a carrier, so we can’t pretend to be neutral — SIPNEX runs VICIdial traffic as its core business, and we score ourselves openly below. The scorecard works whether or not you ever talk to us.
The seven criteria that pick a SIP trunk for VICIdial
| # | Criterion | Pass looks like | Fail looks like |
|---|---|---|---|
| 1 | Dialer tolerance in writing | Terms permit or expressly serve dialer traffic | “Auto-dialing” listed as prohibited use |
| 2 | CPS headroom | Your peak CPS fits without surcharges | Low defaults, discretionary caps |
| 3 | Channel capacity | Channels scale free with usage | Per-channel fees or tiny defaults |
| 4 | Billing increments | 12/6 or similar short increments | 60/60 rounding |
| 5 | Attestation | Carrier signs A-level under its own cert | B/C, or attestation by paperwork only |
| 6 | Short-duration policy | Short calls accepted or clearly priced | Pre-authorization clauses you skipped |
| 7 | US route quality | Low PDD, stable ASR on Tier-1 routes | Grey routes, dead air, spam-flag churn |
1. Dialer-traffic tolerance — in writing
This is the elimination round: a great rate on a trunk that prohibits your traffic is a countdown timer. RingCentral’s AUP bars customers from “auto-dialing or ‘predictive dialing.’” Vonage’s Reasonable Use Policy bars auto-dialing, telemarketing, and call-center activity outright. 8x8’s business terms exclude autodialing and call-center operations from unlimited plans and reserve the right to terminate immediately.
Less obvious: Telnyx’s Acceptable Use Policy lists “auto-dialing or predictive-dialing (sometimes referred to as ‘robo-dialing’)” in its general list of improper uses — not only under unlimited plans. Plenty of dialers run on it anyway; the point is what the paper says when a dispute starts. Our survey of SIP providers that allow autodialers goes vendor by vendor.
2. CPS headroom
A predictive dialer’s defining behavior is bursts of simultaneous call attempts. Telnyx documents a default limit of 20 CPS per source IP or SIP username — excess attempts are rejected with SIP 503 — plus a monthly Outbound Peak CPS surcharge computed from the 95th percentile of hourly peaks: the first 5 CPS free, then $12 per CPS in the 6–25 band, rising to $30 at the top. Telnyx’s own worked example prices a 163 CPS peak at $2,448 per month.
Ask every candidate three questions: what’s my default CPS, what does exceeding it cost, and what happens to rejected attempts?
3. Channel capacity vs. per-channel fees
VICIdial hurls calls at whatever concurrency your campaigns demand. Telnyx starts new accounts at 2 concurrent outbound calls, rising to 10 after Level 2 verification; Telnyx asks for use-case detail before raising limits beyond 100 channels. Twilio, to its credit, charges no per-channel fees — its real cost driver sits in criterion four. Confirm the channel ceiling in writing before load day, and keep a second trunk configured for failover so a cap never becomes a dead floor.
4. Billing increments — where the 60/60 math bites
Twilio bills voice — Elastic SIP Trunking explicitly included — in 60-second increments on standard pay-as-you-go pricing: a 61-second call bills as two minutes. Telnyx voice is 60/60 as well. Dialer campaigns generate thousands of short calls, exactly the workload rounding punishes: an 8-second voicemail hangup bills as a full minute under 60/60, versus 12 seconds under SIPNEX’s 12/6 (a 12-second minimum, then 6-second increments). A 32-second conversation bills as 36 seconds instead of 60.
At dialer volume, increments quietly outweigh headline per-minute rates. Run the math against your own ALOC.
5. A-level attestation the carrier actually controls
Under the SHAKEN standard (ATIS-1000074), A-level attestation means the originating provider knows the customer and their right to the calling number; B means it can’t verify the number right; C is a gateway signature.
What to check: who signs, and at what level. Twilio grants Elastic SIP Trunking calls A-level attestation only after Trust Hub KYC — roughly 24 hours of business-profile vetting plus about 72 for the SHAKEN product — and states it signs “to increase call answer rates.” Skyetel assigns A, B, or C based on the customer’s representations. A carrier holding its own SP certificate signs directly.
Attestation alone is no shield, though: per TransNexus’s March 2026 STIR/SHAKEN statistics, 89.8% of calls authenticated by prolific robocall signers carried A-level attestation, so analytics engines weigh behavior alongside the signature. The A-level vs. B-level breakdown covers what terminating carriers do with each.
6. Short-duration and pre-authorization clauses
voip.ms requires pre-authorization for all telemarketing-type use — automated dialers, call centers, dialer traffic — and may suspend unauthorized use without prior notice, DIDs included. It separately requires pre-authorization for short-duration calls, defined to include calls carrying signal for under 6 seconds. Clauses like these only become traps when you skip them and load a campaign. If a candidate’s terms carry one, get the authorization in writing before the first dial.
7. US route quality and PDD
Everything above is contractual; this one is empirical. Post-dial delay, early-media handling, ASR stability across a full campaign day, spam-label churn on the route — none of it shows up in terms of service. Run a pilot on real leads before committing volume, and measure from your VICIdial reports, not the carrier’s dashboard.
How the carrier categories score for VICIdial
UCaaS unlimited seats (RingCentral, Vonage, 8x8): instant fail on criterion one — the policies quoted above ban the workload. An unlimited plan pointed at a dialer is a suspension with a start date; the unlimited SIP trunk economics post explains why.
CPaaS platforms (Twilio, Telnyx): engineering-grade networks with real documentation. Twilio’s AUP contains no autodialer prohibition — it pushes TCPA and consent compliance onto you — and charges nothing per channel, but 60/60 rounding taxes every short call. Telnyx publishes its CPS mechanics precisely, yet its AUP lists predictive dialing among improper uses and flags low ASR and high abandonment at its own discretion.
Budget wholesale ITSPs (voip.ms, Skyetel, Flowroute): the rates attract dialer operators; the policies vary widely. voip.ms demands pre-authorization. Skyetel’s terms don’t prohibit dialer traffic — they make you solely responsible for TCPA compliance, with consent records kept five years and full indemnification. Flowroute’s terms require compliance with telemarketing and DNC law and take no dialer-specific stance. They are not interchangeable.
Dialer-grade carriers (SIPNEX — bias fully disclosed): the category built for the workload, and we’re in it. SIPNEX is an FCC-licensed carrier: VICIdial traffic is the accepted use, not a tolerated one. Billing is 12/6 on dialer traffic, calls are signed under our own STIR/SHAKEN SP certificate at A-level attestation, and we’re registered in the Robocall Mitigation Database (a filing the FCC requires of every provider).
We don’t publish a termination-rate table — increments and traffic mix make generic tables misleading — so the honest move is to request rates against your actual CDRs. Config lives in the VICIdial SIP trunk setup guide.
Red flags that predict a mid-campaign suspension
- “Unlimited” anywhere in the plan name. Unlimited pricing depends on light usage; a dialer is the opposite, and every unlimited policy quoted above excludes autodialing.
- Prohibited-use language you’re planning to ignore. Traffic flowing today means nothing — the clause activates when your volume gets noticed.
- Discretionary thresholds. Action on “low ASR” or abandonment “as determined by” the carrier makes your campaign metrics grounds for termination at someone else’s judgment.
- Pre-authorization clauses you never invoked. Suspension can arrive without prior notice, taking your DIDs with it.
- Attestation by paperwork. If your signature level rests on representations, verify what your calls actually carry.
If a suspension lands anyway, the dialer account suspension playbook covers the recovery sequence — but the scorecard exists so you never need it.
Frequently asked questions
Can I run VICIdial on an unlimited VoIP plan?
No — every major unlimited policy excludes autodialing. RingCentral’s AUP prohibits predictive dialing outright, Vonage bars dialer and call-center activity, and 8x8 excludes autodialing from unlimited plans with immediate-termination rights. A VICIdial floor on an unlimited seat plan is a breach from the first campaign; metered dialer-grade trunking is the only durable model.
Does Telnyx allow VICIdial dialer traffic?
On paper, no — Telnyx’s Acceptable Use Policy lists auto-dialing and predictive dialing among improper uses, in the general list, not just for unlimited plans. It also flags low ASR and excess abandonment at Telnyx’s discretion, and layers CPS limits and surcharges on top. VICIdial operators do run on it, but the written policy is the reference point if a dispute starts.
How much CPS does a VICIdial floor actually need?
Estimate it from your own campaigns: agents × dial ratio ÷ attempt spacing sets the burst rate, and hopper refills spike it. Then compare against the carrier’s written default — Telnyx, for example, documents 20 CPS per source IP with excess attempts rejected. Get your required CPS confirmed in writing before load day, not mid-campaign.
Why do carriers suspend VICIdial traffic mid-campaign?
Because the traffic finally tripped a clause that was in the terms all along. Common triggers: autodialing prohibitions, discretionary ASR and abandonment thresholds, short-duration rules like voip.ms’s pre-authorization requirement for sub-6-second calls, and telemarketing clauses requiring approval you never requested. Suspension can arrive without prior notice, DIDs included — read the policy before the pricing page.
Does A-level attestation guarantee VICIdial answer rates?
No. A-level attestation is necessary hygiene, not a deliverability guarantee — per TransNexus’s March 2026 STIR/SHAKEN statistics, 89.8% of calls authenticated by prolific robocall signers carried A-level attestation, so analytics engines weigh volume and duration behavior alongside the signature. B attestation reads as a lower-trust signal, but no carrier publishes a specific answer-rate gap. Pair A-level signing with number rotation and clean pacing.
Score your current trunk against the seven criteria — if it fails two or more, run a pilot before your carrier runs the clause. SIPNEX quotes VICIdial-grade trunking against actual CDRs: (833) 665-2220.
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