The Yahoo! Messenger app has received a pretty significant upgrade today -- the app now lets you make video and voice calls to Yahoo! Messenger friends. That has a few interesting outcomes, the first of which is that you can now make video calls from any iPhone running iOS 4.1 to anywhere with a Yahoo! Messenger account, including back to PCs running the client there. We haven't had a chance to try it out yet, but the app is a free download, so you can see for yourself if you want. You can also make free voice calls between friends, or for an extra fee, call out to phones around the world.
One caveat: the calls don't seem to work on the iPod touch 4G, according to reviewers on the App Store. We're not sure why that would be, but the app description clearly states that service is only for iPhone 3GS/4. Otherwise, here's one more solution to voice and even video chatting over 3G on your iPhone.