AT&T, as you may have noticed, is very carefully doling out data throughput these days. Look how long it took for them to activate MMS functionality — and even then, it was a one-toe-gingerly-in-the-water approach, scanning the horizon to see if any of their cell towers would burst into flames.
So the fact that they're now going to offer tethering for their smartphones in general (and the iPhone in particular) is huge news — even as it comes with a reigning-in of data throughput across the board.
AT&T's recent press release detailed a new set of capped data plans advertised as a way to make the online experience more affordable to their customers. The entry-level DataPlus plan costs just US$15.00/month, but limits throughput to 200 megabytes; any overages will take another fifteen bucks out of your pocket for another 200 megs. The Death Star argues that 65% of their smartphone customers use less than 200 MB/month.
Meanwhile, the next-tier DataPro (US$25.00/month for 2GB) — which will replace the current US$29.99/month unlimited data plan offered for iPad 3G's come June 7th — has the option of tethering (i.e. using your phone as a wireless, broadband modem for your computer) for an additional US$10.00/month. Tethering will become available this summer when iPhone OS 4 rolls out.
While all of this appears, on the surface, to be good news, everything really hinges on the robustness of the AT&T data network — which history has shown to be not that robust. (The Death Star's recent move to install free Wi-Fi hotspots in New York City's Times Square is less about customer/tourist convenience and more about how bad the wireless service in the Big Apple is.) It's not enough for AT&T just to have exclusive rights to Apple's two hottest pieces of hardware (the iPhone and iPad) — they have to make sure their customers can USE that hardware, or they will go elsewhere, and the promise of iPhone tethering be damned.