Unless they make the contract voidable (don't supply you with service is about the only sure way), you're stuck.
You could always sell the phone and buy something better, something you could bring to another carrier once the contract is up.
Or keep your eyes open for one of these "we'll pay your ETF" deals that come up every so often. They're usually from carriers that couldn't supply a signal in a steel barn, but every so often one of the biggies matches it. (Then make sure you get a 15 or 30 day trial - in writing and dated, so you can back out if they're even worse.)