Simon Telephonics’ Google Voice Gateway works with VoIP PBXes, such as Asterisk; stand-alone SIP phones, such as those from Polycom and Linksys; and mobile phones with SIP stacks, such as the Nokia n810. Asterisk users are abandoning the native gtalk driver, finding that incoming calls won’t connect, logins time out, and as of Asterisk 10.1, the gtalk audio path is broken. The gateway will get you reconnected using a standard SIP trunk.
TIP: Having trouble with the sign-up process? Make sure you can log in to Google Talk with your Google Voice-affiliated account using a third-party chat client before e-mailing for support.