Didww To Retell

---
name: didww-to-retell
description: >
  Connect a DIDWW phone number to a Retell AI agent over custom telephony,
  with full MCP automation: Retell's official MCP can create agents AND
  import numbers. Use whenever the user wants a Retell agent on a real
  phone number via DIDWW, mentions pairing DIDWW with Retell, custom
  telephony, sip.retellai.com, import-phone-number, or debugging calls
  between the two.
---

# DIDWW to Retell

The most automatable pairing in the family: Retell's official MCP
(`https://mcp.retellai.com`, Bearer API key) covers agent creation,
configuration AND phone number import, and the DIDWW MCP (OAuth) covers
the carrier side. When both are connected, this entire connection is tool
calls with zero scripts and zero dashboards. `scripts/connect.py` exists
only for sessions without the Retell MCP.

## Auth and automation map

| Side | Best path | Auth |
|---|---|---|
| DIDWW (trunks, DID, spend limits) | DIDWW MCP `https://api.didww.com/mcp` | OAuth, no keys |
| Retell (agent, number import, binding) | Retell MCP `https://mcp.retellai.com` | Bearer API key, entered once at MCP setup |
| No Retell MCP available | `scripts/connect.py` | `RETELL_API_KEY` env var |

## The flow

1. **Confirm in one message:** number (or country to buy), agent
   (existing or create from a described purpose), transfer target,
   country allowlists for calls if the user wants them.
2. **DIDWW side (MCP):** inbound trunk with host `sip.retellai.com`,
   transport TCP (Retell's recommendation; UDP packets can get dropped),
   digest auth preferred (Retell has no single stable inbound IP). For
   the outbound leg allow Retell's egress ranges on the DIDWW trunk if
   using IP filtering: `18.98.16.120/30`, `3.42.144.0/23`,
   `153.57.128.0/18` (plus `143.223.88.0/21`, `161.115.160.0/19` for
   some US traffic). Create the outbound trunk, note host and
   credentials, set spend limits (10 to 50 USD/day).
3. **Retell side (MCP or script):** one import call does everything:
   `phone_number` (E.164), `termination_uri` (the DIDWW outbound host),
   `sip_trunk_auth_username`/`password`, `transport`, and the agent
   binding inline via `inbound_agents` / `outbound_agents`. There is no
   separate trunk object to manage.
4. **Verify:** inbound from a mobile, outbound caller ID, transfer.
   Retell's MCP reads call logs for verification without leaving the
   conversation.

## Failure map

- Inbound silent or rejected: digest mismatch, or the DIDWW trunk uses
  UDP where TCP was expected; set `;transport=tcp`.
- Later changes to the trunk (new carrier host, new credentials): Retell
  requires DELETE and RE-IMPORT of the number, not an edit; re-bind the
  agent in the same call.
- Country restrictions blocking test calls: check
  `allowed_inbound_country_list` / `allowed_outbound_country_list` set at
  import.

## Panel map and money

Retell keys: dashboard, API Keys tab (the same key powers their MCP).
Billing tab: prepaid credits with optional auto-recharge; 10 USD free
trial credits. Real cost roughly 0.07 to 0.31 USD/min, and using the
DIDWW trunk zeroes Retell's 0.015 USD/min telephony line: say this, it
is a genuine saving. Warn that subscription items (numbers, knowledge
bases, concurrency) bill the card separately at cycle end and that
calls hard-block at zero credits. DIDWW side: prepaid; top-up,
Auto-charge and Low Balance Notification (OFF by default) in Billing,
Payment Methods.

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Built around [DIDWW](https://www.didww.com/?ref=didww-to-retell) SIP
trunking and Retell's custom telephony docs; verified August 2026.