For incoming call, it would not be an issue. I believe that Qnewbie should be able to get the thing done. Are you using Asterisk programming script in setting up your application or using a GUI?
The gizmo5 account works as expected with method 3 for a while.
The only error I made(as I only use copy&paste style to edit the sip.conf) is the register string, which misses a number in the gizmo5 number. Now it works like a charm.