You mean designed for the new GSM frequency AT&T is adopting instead of supporting one of the existing 3 frequencies that work fine.

Yeah, that's it.

Pretty much what all the carriers have done. Some have used CDMA and TDMA in addition to the GSM variants, but the theme is pretty much the same... Proprietary signal so you can lock customers in. I chose to be locked into AT&T since their coverage is far better than T-Mobile where I live.