Wanting to switch to T-Mobile from Sprint

So first things first, I have a family plan (3 lines) and am still on contract.

So one, I was hoping to find advice on how to get out of my Sprint contract without incurring the ETF. So far I've heard complaining about lack of service at home could work, using a raise in certain fees as leverage to break it, or to tether and download massive amounts of data. Any other suggestions?

Second, my son has an iPhone and he'll want and iPhone if we do make the move. I have a coworker with an AT&T iPhone 4S he would sell me cheap, but I'm not sure with what data speeds could be expected to get on it.