I had this exact problem. I think I found a workaround. Have a look at this thread.
http://forums.androidcentral.com/in...-really-need-disable-t-mobiles-voicemail.html
That's sound like it would take forever for the google voice to pick up. Like 10 rings. I think it's better to get get that voicemail turned off.
I would love for someone to tell my how many rings it takes for google voice to pick up.
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