Together with Apple's new Wi-Fi FaceTime, that's two voice-over-Internet protocol apps to reduce talk time charged to your bill from AT&T, Apple's sole U.S. wireless carrier.

"Video chat may be the next wireless fad," said J.D. Power and Associates wireless analyst Kirk Parsons. "However, it's very much dependent on having the same device -- iPhone 4 in this case -- or customers affiliated with the same carrier, like Skype. So right now it's a small percentage of the total wireless user base, but can take off fast if interoperability between devices and carriers ever becomes a reality."

Unlike Apple's FaceTime, Skype doesn't yet have access to the iPhone 4's front-facing camera, but will still allow voice calls, and video capability can't be far off.

The iPhone 4 is one of the few smartphones to sport both front and back cameras to enable a caller to see the screen and be captured by the camera at the same time, but the feature has emerged on Android-based devices that try to mimic the iPhone experience, like the HTC EVO and some versions of the Samsung Galaxy.

"Front-facing cameras are just beginning to show up in the smartphone segment but still are very far away from becoming mainstream until that capability trickles down to non-smartphone devices and more folks get on data  plans," Parsons said.

Skype also announced that it has abandoned plans to charge a fee for using the service over 3G networks.

"At Skype, we believe that better call quality and better availability (which is achieved with an app capable of multitasking and/or making calls over 3G) lead to increased call frequency and longer calls," the company wrote on its official blog. "We also believe that the mobile world is in a period of significant change; for example, with some operators starting to move to tiered pricing models. In light of that, we no longer have plans to charge a supplement to make calls over 3G."

The new Skype version also allows multitasking so users can operate other apps without disconnecting a call.

Apple last month confirmed that FaceTime users who initiate or receive a standard voice call, then switch to Wi-Fi to use the video-chat app, won't keep accruing minutes for the duration of the call. That's good news for long talkers without unlimited plans who stretch their monthly limits.

There's a catch, though. The next version of FaceTime is likely to work on 3G.