I think I have found right thread to ask this question
I'm trying to configure VOIP service to use with third party voip service (betamax in my case, google voice also works).
First I thought I can configure it to use par with TM with 2 phones as this modem has 2 phone plugs. But voip settings allow one server only.
So I decided to change to betamax setup everything.
1. Router seems to connect back to tm sip servers even if I change settings to different server (hardcoded?).
2. I need to leave outbound servers empty (required by betamax), routers seems to write back tm sip outbound sip even though I remove and apply changes

Any thoughts on how to change SIP settings?