Borrowing an iPhone 4 - I've swapped the sim but can I access my email and iMessages without loosing the owner's? Can I access my mail and iMessages without wiping the iPhone first?  I want to return the phone to its pre-loan state when I'm done borrowing.
You can do this, however you should just back it up to the owners computer first (with iTunes or iCloud). Then wipe the phone and when you are done with it, the owner can restore all of his data.