I called my buddy in China over 3g skype to skype (iphone to his laptop) in July this year and I got a $25 fee from at&t. It was a voice fee too it looks like. Wasn't skype to skype even over 3g free then?
Skype to Skype is just that, doesn't matter what platform you are on. The OP is correct it was free in July, and in fact Skype decided against charging over 3G at all due to overwhelming feedback. I would check with AT&T for sure and see what's up.