When you port your number you need a PIN code as well. Google Voice doesn't provide a PIN code, but if you use the last four digits of the Google Voice number, the port will go through.

or enable the forwarding of text messages to e-mail to view your code. To enable the last option, view your Google Voice account settings, and under the "Voicemail & Text" heading you'll find a ...

Google is increasing the maximum length of its Google Voice PIN codes from 4 digits to 10 ... (Maybe it’s time to fire up the old proxy server, and find a local US telephone number to trick Google ...