I'm curious about the details of the contract between Apple and AT&T, such as who pays whom and under what terms the money is exchanged.

Hi
I doubt if this will ever be made public.... but I suspect it worked like this:

AT&T offered a higher handset price than anyone else to apple, on the grounds of minimum unit sales and exclusive distribution.

They have set up a similar exclusive deal in the UK with O2.

I believe they (Apple) have exclusive distribution deals across the world.

the advantages for Apple are that they do not need to manager the distribution of the product and they have minimum guaranteed sales!

Mike
http://www.rapidbi.com