Before you sell your old iPhone or Blackberry, before you give it away to a friend STOP! 

You need to wipe all of your personal information from that smart phone. Just removing your SIM card does nothing to protect you against identity thieves or others who want your personal information. Here's an article on how to completely wipe and iPhone. Here's another one on how to wipe a blackberry. Simply put, you need to use the software that came with your smart phone to be sure it's clean enough to sell. Better yet, go to the store where you got the phone and have the professionals do it for you.

The same goes for laptops and desktop computers. Deleting your files does nothing to protect you. Formating your drive isn't any kind of solid protection. Use Darik's Boot & Nuke to completely wipe any hard drive.