AgentLine, Retell, Vapi and Bland AI connect software to phone conversations. AgentLine focuses on phone numbers for AI agents, with hosted voice, REST, MCP and a skill. Choose among these platforms by the conversation, integrations and operational controls your workflow needs, rather than assuming one platform is best for every agent.
This comparison is written by AgentLine. Documentation was reviewed on October 18, 2026. We have not measured comparative setup times, latency or conversion rates; the criteria below are a way to run your own evaluation.
Comparison at a glance
| Platform | Documented starting point | Evaluate when | Verify before launch |
|---|---|---|---|
| AgentLine | Hosted phone agent, REST, MCP and skill | An existing agent needs a number, calls and transcripts | Runtime tasks, owner handoff and failure handling |
| Retell | Phone-call API and dedicated transfer modes | Human handoff is central to the workflow | Transfer recipient experience and fallback |
| Vapi | Call API and provider-specific voice configuration | Voice-provider selection matters | Provider settings and call event handling |
| Bland AI | Conversation tools attached to agent prompts | Business API actions drive the call | Tool attachment, outputs and actual writes |
AgentLine: phone access for an existing agent
Create an agent, provision a number and start a call with REST, or use the equivalent connected MCP tools. Hosted voice handles ordinary conversation from your approved instructions. Your external runtime is needed for explicit lookups and tasks; it does not need to generate every spoken reply. Inbound SMS and transcripts are available through the same account. Start with the developer walkthrough.
Retell: evaluate the handoff workflow
Retell documents a phone-call API and cold, warm and agentic warm transfers. AgentLine's transfer is restricted to the configured owner. If your requirement includes briefing a representative before connecting, evaluate that distinction explicitly. The lead-follow-up comparison gives a shared test plan.
Vapi: evaluate voice configuration and events
Vapi's voice configuration uses provider and voiceId. Its server events cover call and tool interactions. AgentLine exposes its hosted voice catalog with voice_id. The voice selection guide explains the difference without treating identifiers as interchangeable.
Bland AI: evaluate business tools
Bland's tools documentation describes conversation-time actions backed by webhooks, code or connected integrations. For a booking workflow, test the actual calendar result and failure handling. The appointment-booking comparison separates intake from a confirmed event.
Compare total cost with the same workload
AgentLine's published rates are monthly plans from $20 with included US or Canada numbers, call minutes and SMS; beyond the plan, $3.00/month per number, $0.12/minute for calls (per-second after a one-minute minimum; zero-second calls are free), and $0.02 per SMS in either direction. Check pricing and your account's allowances before budgeting. Runtime hosting and external integrations can add costs.
Use current Retell pricing, Vapi pricing, and Bland pricing for the configurations you select. Include number rental, voice and model choices, external tools, runtime hosting and billable attempts. A headline per-minute rate is insufficient to compare total cost per successful task.
Make the decision with evidence
Run the same authorized test calls on your own phones. Include a routine answer, interruption, failed lookup, no answer and human escalation. Record prompt versions, call IDs, transcripts, confirmed downstream writes and charges. Choose the platform that meets the workflow's acceptance criteria. For number sourcing or messaging requirements, use the phone-number buying guide and Telnyx SMS comparison.