Reselling a US Cellular Programed Phone

Hello,
I recently went to US Cellular and signed up for a new 2 year contract and bought a new phone (I've been very happy with the company). In the past I've always recycled my old cell phone when I signed a new contract, and was planning on recycling my old Red Razr phone. The salesman said since my phone was in good shape, etc why not try to resell it?

I thought that was a good idea, however I'm not sure how to prep the phone for resale, and looking for suggestions.

Beyond the obvious deleting contacts, texts, photos, etc what else should I do?

It's been my understanding US Cellular doesn't have removable SIM cards, and when I power the phone on it still shows my number, etc (though it won't allow me to place any calls), and that concerns me.

I am new to this and not very knowledgeable, so any advice on how to prep the phone would be appreciated, thanks!

never mind. Called US Cellular, they told me to bring it into a shop and they will wipe the phone. Good info in case anybody else is interested in doing the same, thanks.

Wouldnt you wanna keep a spare phone around just in case?