As rumors over the past week have indicated, Skype’s iPhone app will launch tomorrow and will be available in the app store.

The application will allow users to operate the Skype client from their iPhones. Like Skype’s online service, this will involve free calls to other Skype users and cheap calls (requiring Skype Premium or pay as you go plan) to landline and mobile phones.

This is something in clear and direct conflict with the device’s own core use — making calls. To steer clear of an outright conflict with AT&T’s network, which could have prevented app store approval, the client will only work when connected to a Wi-Fi network.

Even still, the ability to make free and cheap domestic and international calls without eating up minutes is a valuable proposition. Though it’s unlikely that it will disintermediate AT&T service plans (required to activate non-jailbroken iPhones), it could cut into revenue derived from additional fees such as international calling, roaming, overages, etc.

The interesting part is the integration with a device that’s, after all, designed to make calls. Skype’s adoption on the desktop by comparison has been held back by the need to buy and plug in additional hardware (headset or Skype phone). The PC as an instrument to make calls, has been a conceptual leap that has been lost on more “mainstream” users — at least in the U.S.

Integration to mobile makes a lot of sense and will be welcomed by Skype’s loyal user base. It could also help the company tap into new sets of users that are attracted to the idea of cheap international mobile calls. TruPhone is an existing app that has the same idea, but doesn’t have Skype’s brand equity or its 300 million global subscribers.

Skype is trying in lots of ways to redefine itself and its performance as a strategic investment for parent eBay. We’ve been in discussions with the company about some interesting directions to be a better search tool, in addition to a communications tool. At the local level, the two can go hand in hand. More on that soon.