Prove that they broke the contract and you didn't therefore you get out free of charge. You could point out to them that they suck. Why drop them? They drop your calls, is it a way of getting even with them? Flip them off. Send a picture of you cutting the head off the Sprint mascot instead of the check for the bill. Show them how stupid they are by looking for ways to show them that they are.
I work next to the people that recieve those letters. It's absolutely hillarious when customer's draw, paint, stensil, or whatever on their bills to say they are not paying. Everything from middle fingers to reproductive organs. Please keep the laughs on coming.
I agree with this person. If you need to get out of your agreement, do it. Cancel your lines, port your numbers, and pay the ETFs. More than likely you're "done" because of something you don't think you should be responsible for..like your teenager "not" using the internet on their phone EVER because they "don't know how" or calls to another country made by someone you let borrow your phone. Here's a tip for the future. If a phone is in your name, you are responsible for EVERYTHING that is done with it. It doesn't matter who did it specifically, you ARE responsible for it.