Can I trade my phone in for the iPhone 6 or 6 plus?

I have sprint and tecnoically my contact end in August but last year around August my mom added someone on our contact around August or September. Now she said that if I upgrade it would take away my unlimited data! Same with my mom, sister and dad! But I asked my dad about me upgrading and he said thy I can just trade in my phone for the iPhone 6 or 6 plus and just sign a new 2 year contracts I honestly need a new phone so bad. I have the iPhone 4. Lol and it's shattered on the front and back and works so slow and has waterdamage.

I don't think they will take a iphone 4 and if anything you might get 50 dollars

Are you on Verizon? In order to buy an iPhone 6 (or any new phone) and still keep your unlimited data plan, you would have to buy the phone RETAIL. Not through upgrading. Not through contracts. The full retail price (which I believe is $599 for the iPhone 6, $699 for the Plus)

UPGRADING doesn't give you a phone for free either. What it does is it lets you buy a phone for the subsidized price ($199 for the 6, $299 for the Plus) and then agree to a 2 year contract (which would wipe out your old Unlimited data plan)

Long story short: Unless you have $599+tax sitting around, you're not getting an iPhone 6 and keeping your unlimited data (also a broken iPhone 4 only sells for maybe $30-$50)

Recently iphone 4 trade in was $99, thats a good deal, but your contract needs to be up to get a new contract price for 6 or 6+