I do not recall if I have explained this adequately, but, even if I have, I will do it again. Why Apple and AT&T should allow a Skype app on the iPhone.
I do not use AT&T to call internationally on my iPhone. I never will. The cost is horrific. AT&T could change that, but they don't. Thus, I will never, ever, call internationally on my iPhone. Except for when ICA was in Montreal, but, I didn't when I was in France. And I don't call Israel or the UK on it, I use Skype. So, offering international calling on the iPhone via AT&T is a waste of time and probably does not generate much revenue. Sure, some people call internationally, but, iPhone users are connected and have better ways to do this.
Allowing a Skype app would thus not decrease revenues much. However, such an app would be an amazing value-add, and would probably boost sales and thus boost overall use, which would increase revenue.
Imagine if you could offer a cell phone with free international calls, and, in fact, free calls period. Would it sell? Yes, it would. Granted, free only if the recipient of your call has Skype. Not too hard to do (although the Skype interface on Windows is horribly busy and even I had a hard time parsing all the visual cruft it throws at you).
The iPhone is a flat-rate, I pay whether I use it or not. AT&T and Apple get paid, and I get the ability to call internationally (since I don't do that with it now). Win-win.
Right now, with no Skype, and with Skype phones and Android out there in the wild? Lose-lose for Apple and AT&T. And me too.