1. SIP Trunk Settings
- Transport should choose "TCP"
- Username is the "Registration Number"
- Authentication name is the "Registration number + @tel.t-online.de"
- Outbound-Proxy: is the "primary outbound proxy" which provide by Telekom
2) Inbound caller ID reformatting
3) Sip Headers
- Get Caller ID: FROM
- GET DID from: P-Called Party ID
2. SIP Settings
- TCP protocol is required
- SIP endpoint registration timers should be more frequency
2) Session Timers
- Session Timer choose No
P.S: If there is an issue when using CompanyFlex sip trunk on P series PBX just feel free to submit a ticket from our support portal