I had been a LONG time VZW user until Fall 2008 when I jumped ship and moved to AT&T/iPhone heaven. What exactly is the SIM card for and how do I use it? What do I do with my iphone SIM card when/if I sell my iphone? TIA.
The SIM card stores your phone number, contacts, carrier information, etc. The SIM card should stay with the original customer.
I use exchange for contacts, email, calender, etc.
Cool! You should be good to go then even if they give you a new SIM.
In some cases this is true, but not all. It does carry your carrier information but it won't always keep your contacts on there. Some phones store contact information on the phone itself instead of the SIM. Be aware of this because if you use your SIM in a new phone, not all contacts will transfer over.