Want to jailbreak my iphone 4 ios 7, but what will happen to my contract?

Wanting to jailbreak my iPhone 4. But not to ios 7 jailbreak. I'm actually wanting to downgrade my phone to ios 6 with the signed Ipsw provided by a friend. Problem is once it's downgraded it will automatically be jailbroken on ios 6.1.3. What will happen to my contract. I have sprint. 2 year contract and insurance to get my phone replaced for a certain amount of money.

Technically downgrading the phone is a jailbreak. All this does it voids Apple's warranty if it hasn't already expired. As for Sprint, they don't care. You can use a tin can and string for all they care as long as you pay the bill.