Call Transfers
Call transfers allow your AI agent to seamlessly hand off conversations to a human when needed. In Synthflow, these handoffs are managed using the call transfer action.
Synthflow supports four transfer types, each suited to different use cases:
TEL (Phone Number) Transfers
Use TEL transfers for direct handoffs to a phone number in E.164 format. This is the default transfer option in Synthflow, ideal for routing calls to mobile phones, landlines, or call center queues.
TEL URI transfers are confirmed to work with Twilio and Telnyx. If you’re using a different carrier or a self-hosted PBX, TEL URI handling may not be supported. In that case, use a SIP transfer instead, as SIP URIs are more universally supported across carriers and PBX platforms.
Key features:
- Supports warm and cold (blind) transfer modes
- Configurable timeout and transfer messages
- Optional background music during transfer
Learn more about phone number transfers
SIP Transfers
Use SIP transfers when routing calls to SIP-compatible endpoints such as PBX systems, SIP phones, or softphones. SIP transfers use a SIP URI format instead of a phone number.
Key features:
- Works with any SIP-compatible endpoint (Asterisk, FreePBX, etc.)
- Supports warm and cold transfer modes
- Context preservation with conversation summaries
Learn more about SIP transfers
Dynamic Transfers
Use dynamic transfers when the destination number isn’t known in advance. Your agent can fetch the target number during the call using a custom action or a pre-call webhook, enabling flexible routing based on caller input, business logic, or real-time data.
Key features:
- Fetch phone numbers from CRM systems or APIs during the call
- Route to on-call staff based on schedules
- Location-based or tier-based routing
Learn more about dynamic transfers
Phonebook Transfers
For scenarios where you have multiple potential transfer destinations, use phonebooks to manage them in one place. A phonebook allows your agent to transfer to different numbers based on conditions, all from a single action.
Key features:
- Centralized management of transfer destinations
- Conditional routing based on caller input or context
- Easy updates without modifying agent configuration
Transfer Modes
All transfer types support the following modes:
The whisper message in warm transfers is heard only by the receiving agent, not the caller. This allows you to provide context like “Incoming call about a billing dispute” before the agent accepts.
Feature Comparison
Caller ID Behavior
How caller ID is displayed depends on the transfer mode and your telephony provider:
- Blind (cold) transfers: Use SIP REFER, which passes through the original caller’s number. The receiving party sees who is actually calling.
- Warm transfers: Use SIP DIAL to create a new call leg, so the receiving party sees your Synthflow agent’s phone number.
Caller ID passthrough for cold transfers requires your telephony provider to support SIP REFER. Most major providers (Twilio, Telnyx, Vonage) support this, but verify with your provider if you experience issues.
Transfer Failure Handling
When a transfer fails (timeout, busy, no answer), behavior depends on the transfer mode:
For critical transfers, use warm transfer mode to allow graceful failure recovery. You can also configure:
- Timeout duration: How long to wait before considering the transfer failed
- Fallback behavior: What the agent should say or do if the transfer fails
Hold Experience
While the caller waits for the transfer to connect, you can customize their experience:
- Hold music: Enable background music during the transfer wait time
- Transfer announcement: Optionally announce “Please hold while I transfer you” before the music starts
Configure these options in the transfer action’s settings.
