Platforms and telephony
Frameworks, media transport, phone lines and hosted agent builders that tie the pieces together.
Columns 10/32
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Cloudflare RealtimeCloudflare |
Beta | $0.015 | $0.05 | - | No | $0 | Yes | - | No | Yes | Yes | - | Yes | - | Yes | - | - | - | - | Yes | Yes | - | - | - | - | No | No | 0 | 5 | Cloudflare | medium | 2026-10-10 |
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Stream Video & Audio + Vision AgentsStream (GetStream) |
GA | $0.02 | $0.08 | $0.0006 | No | $0 | Yes | $100 | No | Yes | Yes | - | Yes | Yes | - | - | - | - | - | Yes | - | No | - | - | - | Yes | Yes | 0 | 4 | Stream (GetStream) | medium | 2026-10-10 |
LiveKitLiveKit |
GA | $0.03 | $0.08 | $0.01 | No | $50 | Yes | $2.5 | Yes | Yes | Yes | - | Yes | Yes | Yes | - | - | - | 20 | Yes | - | Yes | - | Yes | Yes | Yes | Yes | 0 | 6 | LiveKit | high | 2026-10-10 |
| GA | $0.03 | $0.10 | $0.01 | No | $0 | Yes | - | Yes | Yes | Yes | - | Yes | Yes | Yes | - | - | - | - | Yes | Yes | Yes | - | - | - | Yes | Yes | 0 | 5 | Daily | high | 2026-10-10 | |
| GA | $0.03 | $0.10 | $0 | No | $0 | - | - | Yes | Yes | Yes | - | Yes | Yes | - | - | - | - | - | - | Yes | Yes | - | - | - | No | No | 0 | 4 | Plivo | medium | 2026-10-10 | |
Twilio Media StreamsTwilio |
GA | $0.035 | $0.12 | $0.0044 | No | $0 | Yes | - | Yes | Yes | Yes | - | Yes | - | No | - | - | - | - | - | Yes | Yes | - | - | - | No | No | 0 | 4 | Twilio | high | 2026-10-10 |
Millis AIMillis AI |
GA | $0.04 | $0.09 | $0.02 | No | $0 | - | - | Yes | Yes | - | - | - | - | - | - | - | - | - | Yes | Yes | Yes | - | - | - | No | No | 0 | 4 | Millis AI | medium | 2026-10-10 |
Telnyx Voice AITelnyx |
GA | $0.06 | $0.09 | $0.05 | No | $0 | No | - | Yes | - | - | Yes | - | - | - | 500 | - | - | 500 | Yes | Yes | Yes | - | Yes | Yes | No | No | 0 | 4 | Telnyx | medium | 2026-10-10 |
Twilio ConversationRelayTwilio |
GA | $0.08 | $0.12 | $0.07 | No | $0 | Yes | - | Yes | Yes | - | - | Yes | - | Yes | - | - | - | - | - | Yes | Yes | Yes | - | - | No | No | 0 | 5 | Twilio | medium | 2026-10-10 |
Retell AIRetell AI |
GA | $0.09 | $0.31 | $0.055 | No | $0 | Yes | $10 | Yes | Yes | - | Yes | - | Yes | - | 600 | - | - | 20 | Yes | Yes | Yes | Yes | Yes | Yes | No | No | 1 | 5 | Retell AI | high | 2026-10-10 |
VapiVapi |
GA | $0.09 | $0.15 | $0.05 | No | $29 | Yes | $5 | Yes | Yes | Yes | - | Yes | - | - | 500 | - | - | 10 | Yes | Yes | Yes | Yes | Yes | Yes | No | No | 2 | 5 | Vapi | high | 2026-10-10 |
Agora ConvoAIAgora |
GA | $0.101 | $0.12 | $0.10 | Yes | $0 | Yes | - | Yes | Yes | Yes | Yes | - | - | - | - | - | - | - | Yes | - | Yes | - | - | - | No | No | 1 | 5 | Agora | medium | 2026-10-10 |
Bland AIBland |
GA | $0.11 | $0.16 | $0.14 | Yes | $299 | Yes | - | Yes | - | - | Yes | Yes | - | - | - | - | - | 50 | Yes | - | Yes | - | - | - | No | No | 1 | 5 | Bland | high | 2026-10-10 |
SynthflowSynthflow AI |
GA | $0.13 | $0.24 | - | - | $2,500 | No | - | Yes | - | - | Yes | - | - | - | - | - | - | - | - | - | Yes | - | - | - | No | No | 1 | 3 | Synthflow AI | low | 2026-10-10 |
SignalWire AI Agent (SWML)SignalWire |
GA | $0.163 | $0.168 | $0.16 | Yes | $0 | - | - | Yes | - | - | - | - | - | - | - | - | - | - | Yes | - | Yes | - | - | - | No | No | 0 | 4 | SignalWire | medium | 2026-10-10 |
| GA | - | - | $0 | No | $0 | Yes | - | No | - | - | - | - | - | - | - | - | - | - | Yes | Yes | Yes | - | - | - | Yes | Yes | 0 | 4 | OpenAI | medium | 2026-10-10 | |
TEN FrameworkAgora / TEN community |
GA | - | - | $0 | No | $0 | Yes | - | No | Yes | Yes | Yes | - | - | Yes | - | - | - | - | Yes | - | Yes | - | - | - | Yes | Yes | 0 | 4 | Agora / TEN community | medium | 2026-10-10 |
ThoughtlyThoughtly |
GA | - | - | - | - | - | - | - | Yes | - | - | - | - | - | - | - | 34 | - | 10 | - | - | Yes | Yes | Yes | - | No | No | 0 | 3 | Thoughtly | medium | 2026-10-10 |
| Beta | - | - | $0 | No | $0 | Yes | - | No | - | - | - | - | - | - | - | - | - | - | Yes | Yes | - | - | - | - | No | Yes | 0 | 3 | Vercel | low | 2026-10-10 | |
Voiceflow (voice agents)Voiceflow |
GA | - | - | - | - | - | Yes | - | Yes | - | - | Yes | - | - | - | - | - | - | - | Yes | - | Yes | - | - | - | No | No | 0 | 3 | Voiceflow | low | 2026-10-10 |
Vonage Voice/Video API AI connectors (Audio Connector) + AI StudioVonage (Ericsson) |
GA | - | - | - | No | $0 | - | - | Yes | Yes | Yes | Yes | - | - | - | - | - | - | - | Yes | Yes | Yes | - | - | - | No | No | 0 | 4 | Vonage (Ericsson) | low | 2026-10-10 |
LayercodeLayercode, Inc. |
Deprecated | - | - | - | - | - | - | - | No | Yes | - | - | - | - | - | - | - | - | - | Yes | Yes | - | - | - | - | No | No | 1 | 2 | Layercode, Inc. | medium | 2026-10-10 |
PlayAI AgentsPlayAI (acquired by Meta) |
Deprecated | - | - | - | - | - | - | - | - | - | - | - | - | - | - | - | - | - | - | - | - | - | - | - | - | No | No | 1 | 2 | PlayAI (acquired by Meta) | medium | 2026-10-10 |
A dash means the vendor does not say. Latency is the vendor's own claim, not our measurement. Per-minute figures are estimates from list prices; each API page explains the basis, because vendors bill by tokens, characters, connection time or flat minutes.
Category warnings
These apply to most APIs in this category.
Headline per-minute price is almost never the all-in price
Most platforms quote a platform or orchestration fee, then pass through speech-to-text, LLM and text-to-speech costs, then add telephony on top. Example: Vapi's $0.05/min is hosting only; its own estimator puts 1,000 minutes at $82-$129 before Twilio/Telnyx minutes. Retell's $0.055/min voice infra excludes the LLM, TTS upgrades and $0.015/min telephony. Budget = platform fee + STT + LLM + TTS + carrier minutes + phone number rental + add-ons (knowledge base, denoising, PII redaction, branded caller ID).
FCC 2024 ruling: AI voices count as 'artificial voice' under the TCPA
The FCC Declaratory Ruling of 8 Feb 2024 confirmed that calls using AI-generated or cloned voices are 'artificial or prerecorded voice' calls under the TCPA. Outbound AI calls to consumers need prior express consent (prior express written consent for telemarketing), must identify the calling entity, and telemarketing calls must offer an opt-out. There is no carve-out for AI that behaves like a live agent. Violations expose you to FCC fines, state AG suits and private TCPA class actions. Inbound calls where the consumer called you are a different, lower-risk situation. Not legal advice; check current rules and state laws (several states add their own AI-disclosure or telemarketing rules).
Call recording and AI disclosure consent
Several US states (for example California, Florida, Pennsylvania, Washington, Illinois) require all-party consent to record, and most voice-agent platforms record and transcribe by default. In the EU/UK, recordings and transcripts are personal data under GDPR. Play a short disclosure at the start of the call ('this call is with an AI assistant and may be recorded') and turn recording off where you do not need it.
HIPAA needs a BAA with every hop, not just the platform
A platform BAA does not cover the STT, LLM, TTS or carrier vendors it calls on your behalf unless they are inside the BAA scope. Some platforms charge heavily for it (Vapi lists HIPAA as a $2,000/month add-on; Thoughtly offers HIPAA/BAA only on Enterprise). Confirm the exact list of covered sub-processors before sending PHI.
Billing rounding, minimums and silence
Telnyx estimates exclude per-call rounding to 60-second increments; Agora rounds SIP/PSTN agent calls up to the next full minute; Bland charges a $0.015 minimum per outbound attempt and per failed call on its telephony; Retell bills per second but keeps billing during silence and hold. Short, high-volume outbound campaigns can cost several times the headline rate. Set max call duration, silence timeouts and voicemail detection so you do not pay agent minutes to talk to an answering machine.
Concurrency caps on entry tiers
Entry plans cap simultaneous calls: Vapi 4 on the free package (10 on Core, $10/line/month extra), Retell 20 included ($8 per extra concurrent call per month), Bland 10 on Start, LiveKit Cloud 5 agent sessions on Build, Thoughtly 10 on Flex. Campaign dialers hit these immediately; calls over the cap are queued or rejected.
Outbound numbers get spam-labelled
Carriers score outbound numbers with STIR/SHAKEN attestation plus call analytics. New numbers that place many short calls quickly show as 'Spam Likely' and answer rates collapse. Register numbers with the carrier analytics registries, keep volume per number reasonable, use numbers your platform can sign with full (A) attestation, and consider paid branded calling (Twilio lists $0.12/call, Retell $0.10/outbound call).
Phone audio is 8 kHz narrowband
PSTN legs are usually G.711 mu-law at 8 kHz (Twilio Media Streams, many SIP trunks). STT accuracy drops versus 16 kHz web audio, TTS is downsampled, and you must resample correctly (sending 16 kHz or 24 kHz PCM into an 8 kHz mu-law stream produces chipmunk or garbled audio). Pick telephony-tuned STT models and test with real phone calls, not browser demos. Plivo and some others offer 16 kHz linear PCM streams if your trunk supports it.
WebRTC needs TURN, and corporate networks block UDP
Browser and mobile agents fail silently behind strict NAT or corporate firewalls without a TURN relay (ideally TURN over TLS on port 443). Managed SFUs (LiveKit Cloud, Daily, Cloudflare, Agora, Stream) include this; self-hosted setups must run and pay for TURN egress themselves.
Echo and noise cause self-interruption
On speakerphones and laptop speakers the agent hears its own TTS and barges in on itself, or background noise triggers false turns. Keep browser echoCancellation/noiseSuppression on, use server-side noise cancellation (Krisp in Pipecat Cloud, ai-coustics/BVC in LiveKit, Retell 'Advanced Denoising' at +$0.005/min), and tune interruption sensitivity.
Vendor churn is real in this category
PlayAI was acquired by Meta in July 2025 and play.ai no longer resolves (checked 2026-10-10). layercode.com and docs.layercode.com now redirect to toyo.ai. The FTC sued Air AI in August 2025 over claims about its AI sales agents. Synthflow removed public self-serve pricing (Enterprise from $30,000/year). Keep prompts, tools and call logs portable, and prefer frameworks (Pipecat, LiveKit Agents) or platforms with export APIs if lock-in worries you.
Latency figures are vendor claims
Every vendor publishes a best-case latency number. Real response time depends on the region of the telephony edge, the agent worker, and each model endpoint. Co-locate them and measure p50/p95 end-of-speech to first-audio on real calls before choosing.