I am going to have to try this setup out. My question is dealing with when you are placing calls and people are calling you. Do they just dial your number and it routes through GV to your phone, or you have to use the GV number that is created? Likewise when you call out what number is it going to reflect to the other person?
If I understand this whole process correctly, GV is the interface number and application for the VOIP service, but can't achieve true VOIP without this workaround.
So to answer your question, you would have people call your GV number which routes them through to your sipgate number that GV is linked to. Outgoing will interface with GV, your sipgate number and use sipsorcery to do the actual routing to the receiving end. Kind of like a switchboard. Now what I don't get (yet) is what number people will see on their caller IDs. Is it your GV number or sipgate number? In the sipgate settings you can tell it what number people will see, but I don't know if that matters in this type of setup. Correct me if I'm wrong.