Moving data from NEW iPhone to OLD?

I had my iPhone 4 stolen and I want to use my old 3GS till I get a new one. When I plug it in, it only lets me back it up with data from my last backup with the 3GS and nothing from my newer phone. I know how to backup and move onto a new phone… But moving back seems to be causing me issues?

Most people just plug their new iPhone into iTunes and let iTunes restore the last backup onto it.

Since your PIM data is on MobileMe, you have the option of starting clean with your iPhone 4, but you're going to lost every setting in every app that you've installed. You'd just sign in with MobileMe, which will download your PIM stuff, then plug into iTunes and reinstall all of your apps…