I tried this : *5005*86*123456789# "123456789" is replaced with number of my choice. I have youmail account and is connected to my phone number right now. Every time I call my voice mail from phone app it says that I have no voicemail( I do but it's on the youmail account) the default number is useless to me right now. Also the youmail number to access my voicemail is 10-digit. But the method I found above is only limited to 9digits. I tried putting 10 digit in and press the call button, the screen flicker every time I press call. Is there anyway I can go into the system file w/o jb to change the default number to the 10 digit youmail number? Btw, i have factory unlocked 3GS on tmobile. Thanks!!