yahoovideochatApple has based a great deal of its iPhone 4 marketing blitz around its so-called FaceTime video calling technology.

But Yahoo is about to challenge Apple for the mobile video calling crown, with plans to brings video chat to iPhones and Android-based phones via its popular Yahoo Messenger instant messaging service.

During a briefing with Reuters on Thursday, David Katz, Yahoo’s VP of Mobile for the Americas region, let it slip that the company will soon be offering mobile app versions of Yahoo Messenger with built-in video calling capabilities.

Earlier this week, T-Mobile announced that its new 4G myTouch smartphone would come with a built-in Yahoo app for video calling. But the availability of standalone video chat apps for a broader set of camera-equipped smartphones could position Yahoo to play a much bigger role in the mobile market.

The free app, will be available for both iPhone and Android phones and will allow smartphone users to not only conduct video calls with each other, but with anyone that currently uses Yahoo Messenger for video calls on their PCs, Katz said (Messenger has 81 million users worldwide, according to Yahoo).