Best Outbound SIP Trunk Providers for AI Voice Agents (2026)

Before comparing brands, weigh these against your use case:

• Cost model and billing granularity. Pay-as-you-go vs prepaid, and per-second vs per-minute (per-second matters a lot for the short calls typical of outbound campaigns).
• Coverage where you actually call. A‑Z termination quality varies by region; a provider strong in the US may be weaker in, say, Africa or the Middle East.
• Codec and media fit. G.711 support avoids transcoding in the AI pipeline; SRTP/TLS for encryption.
• Caller-ID (CLI) control and number validation (HLR) for clean, compliant outbound.
• Concurrency and CPS for campaign spikes.
• Contracts and commitments — some providers discount for monthly commitments; others are fully no-contract.
• Inbound (DIDs) — needed only if your agent also receives calls.

Twilio Elastic SIP Trunking. The default choice for many teams thanks to the broadest feature set, documentation, and integrations. It's a usage-based model that's powerful but typically the most expensive per minute, and it shines most for US-centric deployments.

Telnyx. Runs its own private global IP network, which tends to translate into lower rates than Twilio and deeper troubleshooting. Class-leading elastic SIP trunking and strong compliance, with a steeper learning curve aimed at technical teams.

Plivo. A mature CPaaS with a clean API and transparent per-second billing in 2026. A solid middle option for teams that want simplicity and competitive pricing without owning infrastructure.

Bandwidth. A Tier-1 carrier in the US that underpins major UCaaS platforms. Best for high-volume, carrier-grade US/Canada voice; less of a fit if your traffic is heavily international.

Bitcall. A self-service, prepaid telecom platform built for outbound today. A‑Z termination from $0.01/min with per-second billing, no contracts or minimums, card/PayPal/crypto top-ups, CLI control and HLR validation, and routes tuned for emerging markets (Africa, the Middle East, Asia) as well as Europe. The honest caveat: Bitcall does not offer inbound numbers (DIDs) yet — inbound is on the roadmap — so it's a strong fit for agents that make calls, not (yet) for agents that need to receive them.

• You only need outbound (campaigns, reminders, sales, surveys): prioritize per-second billing, A‑Z coverage where you call, and no contracts. Bitcall, Telnyx, and Plivo all fit; Bitcall is especially competitive for emerging-market destinations and crypto/prepaid billing.
• You need both inbound and outbound now: choose a provider with inbound DIDs today (Twilio, Telnyx, Plivo, Bandwidth). Revisit Bitcall once its inbound launches.
• You're US-heavy and want carrier-grade reliability: Bandwidth or Twilio.
• You want the deepest ecosystem and don't mind paying for it: Twilio.
• You have telecom engineers and want owned-network value: Telnyx.

Whichever you pick, the AI-voice fundamentals are the same: use G.711 to avoid transcoding, keep the media path short for latency, and configure RTP keepalives so calls don't drop during the agent's thinking gaps (see AI voice calls dropping after 30 seconds).

What's the best SIP trunk for a Vapi or Retell outbound agent? The one that matches your volume, destinations, and billing preference. All three of Telnyx, Plivo, and Bitcall are competitive for outbound; Bitcall adds per-second billing, no contracts, and crypto/prepaid, with strong emerging-market routes.

Is per-second billing actually better than per-minute? For outbound AI campaigns with many short calls, yes — per-second billing avoids rounding every call up to the next minute, which adds up quickly at scale.

Do I need inbound numbers (DIDs) for an outbound agent? No. If your agent only places calls, you don't need inbound DIDs — you need good outbound termination and caller-ID control.

Can I use any of these providers with my AI platform? If the platform supports BYOC / a custom SIP trunk (Vapi, Retell, Bland, and others do), yes — you connect the carrier as your trunk.