I can't see the lawsuit getting very far, especially since (former) members of the iPhone Dev Team have publicly admitted that it was their
flawed code, and not malicious intentions on the part of Apple, that caused the unlocked iPhones to be bricked.
I also have a hard time feeling sorry for the owners of the bricked phones, since they knew that unlocking their iPhone was an unsupported hack. Unsupported hacks are often broken by future updates to the hacked code. If losing use of their phones was too great a risk, they shouldn't have hacked them. Don't gamble if you can't afford to lose.
On the other hand, after reading the iPhone warranty a few times, I can find nothing in it that states the warranty is voided by installation of unauthorized software
unless the hardware is damaged as result of that software. Firmware is not hardware. Just about every state in the US has legislation that effectively creates an implied warranty that if a company sells a product, the customer has a reasonable expectation that that product work as advertised. Warranties implied by law always trump manufacturers' warranty limitations and restrictions. Apple may not have a responsibility to make sure US customers can unlock their iPhones for other carriers, but they
do have a legal responsibility to make sure that iPhones (without hardware damage) will work on an AT&T network.
From what I have read, while there was only minor functionality change with the update, the underlying code underwent significant change. I think Apple has planned all along to release an SDK for the iPhone, but they wanted to wait until they had worked some bugs out of the code first. This was the first version of Apple's first phone. I don't believe Jobs or Apple were so naive as to believe the code would be bug free. Remember Cheetah? I also believe Apple would be more than happy to let users use the iPhone on other networks, but breaking into the telecommunications market required them to partner with an existing telecom company. As that partner, it is AT&T who is standing in the way of using the iPhone with other carriers. I seriously doubt the monthly payments Apple receives from AT&T are worth more than the lost market share of people who would buy iPhones if they could use a carrier other than AT&T.