What are the advantages to having a SIM in my cell phone or PDA?

You have to check with your service provider (like AT&T among others) on specifics, but there are a number of general advantages to having a SIM in your cell phone. The SIM gives you global roaming so that you can use your same phone and number when traveling internationally. The SIM is removable so it can help you to switch between devices or to a new phone without losing any of your data, like your phone book, as long as you stay with your current service provider. Its inherent security and brains protect your phone subscription from fraud, and secures your wireless services.