Q&A: I want to use DECT phones with this library, but it is not working! - Aypac/Arduino-TR-064-SOAP-Library GitHub Wiki

You can refer to the Caller/Doorbell Example on how to write the code. It is furthermore important if you want to use the DECT-phones to activate 'Click to dial'/'Wählhilfe' (see screenshots below). Don't forget to click apply/save ;)

Thanks, kirk-loeten for pointing this out!