Porting to Google Voice's voicemail
To activate Google Voice voicemail for your mobile phone, first sign up for a Google Voice account. During account creation, you can either select a new phone number, or automatically have Google Voice integrate voicemail with your existing mobile phone number. If you choose to have Google Voice integrate Google voicemail with your existing phone number, follow the instructions provided during account creation.
If you choose to select a new Google Voice phone number, or already have a Google Voice account, simply log in to Google Voice. Select Voice settings from the Settings drop-down menu at the top right. Under the Phones tab, ensure that you have a mobile phone number listed under the Forwards to area. If you do not, click on Add another phone and follow the directions provided.
Find the mobile phone number that you wish to add Google voicemail to, and click on Activate Google voicemail on this phone. A window will pop up describing the specific steps to complete based on your carrier. In most cases, this will involve dialing a special number which includes your Google Voice number.
Instructions for some popular carriers are provided below. In these instructions, the example phone number is 555-555-1234. Substitute your own mobile phone number when dialing.
For AT&T, dial *004*15555551234#
For Sprint, dial *285555551234
For T-Mobile, dial *004*15555551234#
For Verizon Wireless, dial *715555551234