For me, ATT and verizon plans cost well over $100 for the 2 phones setup like I have and I can't even get 3g speeds from ATT anywhere near me. Last I ran an apples to apples comparison of what I get with Sprint, compared to ATT and VZW, the highest price was Verizon, then ATT, both over $115 befor taxes and fees, while with Sprint, I pay $96 including fees and taxes. Yes, I get a discount with Sprint, but ATT said they'd match it and it was still about $25 more per month. Which might be worth it with ATT if they can infact meet the claimed 7mbps (correct me if I'm wrong on this number) speeds they claim they support with the Iphone, but unless the coverage is here, it's a moot point.
As for ATT and unlimited use, well it's unlimited use of what they allow you to use correct? Did they ever relax the slingplayer restrictions? I have not followed it. Not saying ATT is evil and everyone else is better, every provider has their faults.
Edit:
here's my breakdown of my plans from the 3 providers
Verizon Premium Connect 2 lines, 1400 minutes $159.99 Not sure when Nights and Weekends start, so hard to say if it would cost more than listed already.
AT&T For just 1 iPhone, their online system told me $139.99 to match the features I get with sprint. Again, for just 1 phone.
Sprint before my discount for 2 phones, unlimited data, text, and 1500 talk (barely scratched anymore with the anymobile anytime feature) $129, but due to corporate discounts, loyalty rewards etc, only $96.xx after taxes and fees. Yes, like I said ATT said they would match it, but only on 1 phone, not a family plan.