I commute via rail, and so I've always been interested in adding tethering to my cell phone plan. I figure it'd be a good way to spend my commute other than, um, reading literature.
And now that the iPhone has tethering capabilities, I figured its my perfect opportunity to get more by spending more. Sadly, AT&T hasn't announced its tethering plan yet, but I decided I can infer some information from their existing plans.
I did some research today on AT&T's website, looking into the tethering options for devices they sell now, such as the BlackBerry. I "made" a 450 minute voice plan and added tethering... and the total monthly fee came to $99.99 per month. Certainly more than the $69.99 plan, but clearly tethering will use lots more bandwidth. I also noted that AT&T has a 5 GB cap on their tethering plan.
As a cost comparison, I went to Verizon's online store. They didn't have a tethering option readily visible, so I just made a $450 smartphone plan, and it came to $69.98 per month. Then, I located the Broadband Connect page ... and it suggested that adding tethering to the $69.99 smartphone plan would cost an additional $15.00 per month.
So, if all my math is correct, it seems like for a 450 minute smartphone plan with 5 GB of tethering, the score is: Verizon: $85/mo. AT&T: $100/mo.
One reason why I've liked AT&T is that I knew they were a better deal for the money. Hopefully they'll address this major pricing discrepancy with their competitors. Otherwise, for $15 per month, I may as well go back to Verizon and use my jailbroken iPhone as a client ;-)