Are contacts stored in a sim card?

My daughter is selling her unlocked iphone 3gs and I'm wanting to know if all her contacts are stored on the sim card or does she need to write them down.

There's more than one setting, you'd have to look to see if it was set to save on the phone or on the sim card.

Well you don't sell the SIM with the iPhone. You keep that. It has your number.

As far as contacts being on it, it is an option, though most don't choose to keep them there since it is limited as to how much you could store.