We are using a Twilio-owned Netherlands (+31) numb...
# ❓・ai-evy-supportj
jay22
01/04/2026, 5:34 PM@AI Evy We are using a Twilio-owned Netherlands (+31) number imported into Retell.
In our current setup, live call transfers to another Netherlands number fail with a permission error.
Can you confirm whether live call transfers to NL numbers are supported today when using custom telephony with Twilio (Twilio originates the outbound leg), or whether this is still restricted regardless of number ownership?
If supported, what specific Retell + Twilio configuration is required to ensure Twilio (not Retell) initiates the transfer?
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AI Evy
01/04/2026, 5:35 PMThanks for tagging me @jay22. I'll look through relevant sources and get back to you shortly.
AI Evy
01/04/2026, 5:35 PM### Answer
Based on the available documentation, here's what I can confirm:
Call Transfer with Elastic SIP Trunking
When using imported numbers via elastic SIP trunking (your setup) , call transfer functionality is supported. [(1) ]() The documentation states: "Will I be able to transfer call using SIP trunking? Yes you can use the transfer call feature with SIP trunking."
Key Configuration Requirements
For cold transfers with the transferee's number showing as caller ID, you need to configure your SIP trunking provider (Twilio) to:
- Allow SIP REFER
- Enable PSTN transfer
- Set the transferee's number to show as caller ID
International Dialing Permissions
The permission error you're encountering is likely related to Twilio's geographic permissions configuration. The documentation mentions: "If you need to set up dialing to international countries, search 'geo' to find the 'Voice Geographic Permissions' setting." [(2) ]()
What the Documentation Does NOT Confirm
I don't have explicit documentation confirming whether NL-to-NL transfers are specifically supported or restricted when using custom telephony. The permission error could stem from:
1. Twilio's Voice Geographic Permissions not being enabled for Netherlands
2. SIP trunk termination settings not configured for NL destinations
3. Twilio-side restrictions on international/regional transfers
Recommended Next Steps
1. Check Twilio's Voice Geographic Permissions to ensure Netherlands is enabled
2. Verify your SIP trunk termination settings allow calls to NL numbers
3. Review Twilio's logs for the specific permission error details
If the issue persists after verifying these settings, I'd recommend reaching out to Retell
AI Evy
01/04/2026, 5:35 PM
To learn more, see the sources I considered:
[[1] Custom Telephony Overview](https://docs.retellai.com/deploy/custom-telephony)
[[2] I’m trying to use a toll-free number (connected from Twilio through a SIP trunk)](https://retell.discourse.group/t/i-m-trying-to-use-a-toll-free-number-connected-from-twilio-through-a-sip-trunk/127)
AI Evy
01/04/2026, 5:35 PMFeel free to tag @AI Evy with additional questions. I also appreciate feedback, it helps me improve.