Many thanks to fitwxc for helpful infomration on ip phone.
I read all your articles and setup the following and everything works fine for a couple of weeks until yesterday.
VoipDiscount for outgoing calls, callid was set to my GV number
GV+Sipgate for incoming call, call ID is set to my GV number also
In GV, the forward number is sipgate number.
Call IDs of outgoing and incoming calls are correct.
I use my ata phone to call GV number to check voice mail no problem. Yesterday when I changed GV setting to avoid pin if called from sipgate number, after a few tones then became silent. So I changed back to still asking pin. Then I always getting "the number is discnected or not in service".
Now I have to use my cell phone to call GV# to check VM. I used Tmobile prepaid plan. This means I have to pay to check GV VM.
Anything could be wrong in my setting? I search this forum but found no similar issues discussed.