Skype has release the Skype app version 2.0 which can be used over 3G network on the iPhone and iPad. But not all is rosy. Skype to skype calls through 3G will be charged this September.
Previously from Skype blog: Last Thursday, Apple introduced the iPad, which we’re very excited about here at Skype. The SDK (Software Development Kit) which Apple provides to developers like Skype, has been upgraded for the iPad. The new version, 3.2, removes the restrictions on calling over 3G, which is great news.