I remember these phones had some interoperability issue: https://answers.microsoft.com/en-us/mobiledevices/forum/all/nokia-e72-sip/1ae79fc1-7e0e-4fe5-87c5-aa9d8

I remember these phones had some interoperability issue: https://answers.microsoft.com/en-us/mobiledevices/forum/all/nokia-e72-sip/1ae79fc1-7e0e-4fe5-87c5-aa9d8ae9c7a7 https://answers.microsoft.com/en-us/mobiledevices/forum/all/... (technically all according to specification, but often not working for incoming calls). At the time Symbian was supported by pjsip though.