Skype is working on updating its iPhone app to include the functionality to work over AT&T 3G network. AT&T and Apple just started allowing VoIP app developers to make calls over the carrier’s 3G network, a feature that was missing before. Users believed the main reason for that was to avoid putting additional strain on AT&T’s network, which was already struggling to keep up with extensive data usage. With AT&T investing $18-$19 billion in 2010 to upgrade its network, perhaps that has changed.

Skype said it’s working on final changes to make the app available soon. The company said 3G calls will have CD-quality sound and an indicator with red, yellow and green indicator that will show users the kind of signal they are getting over 3G in real-time.

“We want to give you as much feedback as possible about what’s actually going on with your call,” said David Ponsford, iPhone Team Lead, Skype.