Skype is Skype with a huge S because of its Skype-to-Skype calls - because they are free. Skype-to-Skype calls will no longer be free for those using the iPhone over 3G, by the end of the year. This will happen with the newly released Skype 2.0 for the iPhone. Besides some improvements, the major enhancement with Skype 2.0 for the iPhone is the ability to make and receive calls through 3G, something that wasn't before, mainly due to lack of support.
Finally, isn't 3G more of a problem than a facilitator for voice? Keep aside the 3G data plan you have to pay, making voice calls (even Skype-to-Skype) over 3G on the iPhone will cost money, at a time when it was practically taken for granted that voice calls over IP between users of the same service (here Skype-to-Skype) are always free. Skype 2.0 for the iPhone links: information and download.