Talktatone Makes Free Google Voice/Gmail VoIP Calls on Your iPhone
Gmail users can make free Google Voice calls, but why should they have all the fun? Talkatone sets up free VoIP calls, over 3G or Wi-Fi, from your iPhone, iPod, or iPad through Google Voice for free.
Talkatone does quite a few other neat things with your Gmail account and free voice-over-IP technology, but the main reason it's exciting is a feature that's somewhat tucked away. Double-tap on the Contacts header, and you'll get an option to make a Google Voice VoIP call. Choose a contact or dial a number, and you're calling. If it doesn't work on your first shot, you may need to do a little Gmail-to-Talkatone setup, described at the CyberNet News blog. Otherwise, it's a remarkably simple way to make a free Gmail phone call outside of Gmail.
Talkatone is a free download for iPhone, iPod touch (second generation and later), and iPad, and requires iOS 4.0 and later.