I checked out Cricket's coverage in my area, and it's pretty solid from what I see on their website's coverage maps
Those who want a prepaid iPhone on other carriers can still buy straight from Apple and bypass the contract.
I've been month-to-month on all of my iPhones since they first launched, and now that Cricket is partially subsidizing the initial cost of a new iPhone w/o contract, I see even more people who'll consider skipping the contract.. especially when combined with a reasonable monthly service rate that you could cancel anytime.
I've used Cricket for years before switching to an iPhone, and was very happy with service and rate plans. Given the additional perk of unlimited talk, text, and data, I think that Cricket will sell a ton of these.