since you are out of contract there is a loophole.
basically you port your number over to a prepaid line preferably a gsm service company. I highly recommend a 'Go Pone' from at&t.
http://www.walmart.com/catalog/produ...i_sku=12456294
in other words find the cheapest prepaid phone that includes minutes if possible, but you might need to buy minutes, I remember before some had starter minutes, now it's rare.
http://www.amazon.com/AT-3G-Card-Pre.../ref=pd_cp_e_1
once your number is ported to at&t your sprint 99.99 plan account is canceled automatically.
after waiting 10-15 days:
go back to the sprint.com/sero site and open your account, pick your plan, pick your phone, and pick port option, it will ask you to enter your account number, cell number, pin from your go phone information.
you get your free phone in two days, hopefully phone number is ported, if not just call to see the status, in three-five days if not sooner your old number is ported back into your sero sprint line no questions asked.
your old sprint 99.99 plan with old number>ported to prepaid go phone>ported back to sprint sero account. swap your tp2 into you sero account and sell free phone and enjoy your savings...