if the phone and the sim card no longer have service and the phone has been erased, i wouldn't really stress about sending the sim card. a lot of cash for phones place want the sim card removed
maybe there might be a good reason to remove it still???
in the old days, before smart phones like the iPhone came out, your phone book and your text messages were stored on the sim card. i don't think this is true anymore.. if you have a dumb phone you want that sim card destroyed. heh
the sim card might still have personal information on it.
in the days of sim cards, they are now mostly used to securely authorize your phone's connection to the network and to hold and maintain a list of cell phone towers.. oh yeah almost forgot. also to encrypt your transmissions