I tried the same exact thing. Got my number ported over from ATT and attempted to return my Evo before the 30 days and buy a cheap used phone in the meantime so I could preserve my "upgrade" and buy the Epic for the subsidized price. Turns out it doesn't work that way. The whole sprint 30-day guarantee thing applies to your service as well as your phone so that if you don't like the service, you can return your phone and cancel your service and be refunded your activation fee and price of phone and they'd waive the ETF. They won't allow you to give your phone back and keep the line open. Only people that are actually eligible for an upgrade (not simply opening a new line) can return their phone, keep the line open, and still have their "upgrade" reset. The only other option for new customers is to open another line of service however chances are that you'd lose your phone number (which wasn't an option for me). And to whoever suggested cancelling the contract and opening up another account, I believe sprint has a mandatory waiting period in place for just that scenario. I ended up keeping my Evo beyond 30 days and selling it on ebay for a considerable amount. Assuming the Epic's retail price is the same as what even used Evo's are going for on ebay, no money should have to come out of pocket.