Should I keep my old iPhone or sell it?

So I bought the 3G iPhone because it was cheaper and had more memory and was super sexy. I really love it but Im still really attacted to my old iPhone for sentimental reasons. A girl I work with wants to buy my old iPhone for $200 and before I got the 3G one I told her that I would sell her my old one. Now the time has come and I can’t bear to part with it. I don’t need the money, I would just spend it on clothes or something. But I have this feeling that I shouldn’t sell it and should just keep it as a little keepsake, a keepsake I paid $600 for. And in case something should happen to my 3G, I could always go back to my old phone. Am I crazy to be so attached to an inanimate object? I really to love my iPhone and if I sold it, I think I might really regret it but I feel selfish keeping it. Any thoughts?