Most of @BlinkThinks setting would apply for N9. If you just use the settings from simonics and plug them into N8XX Sip app you should be good to go. That being said I have found that inbound calls don´t always connect on the first, second etc try (I have 4 phone numbers tied to GV). To get around this problem I still use my sipgate sip account (impossible to get now) also with the simonics sip, sipgate answers and simonics calls.

Now the outbound calls work just about 98% of the time with no callback. When I make outbound calls the ringing on my end starts about 10+or- seconds before my party hear their phone ring. For me it´s no deal breaker, also the call is clear on both ends (cable internet or WiMax)