Phones with SIM cards can store contacts directly on the SIM card, as opposed to just on the phone memory unlike CDMA phones where you can only store them on the phone. This makes it extremely easy to transfer contacts between phones (just swap the card, and your new phone has all your contacts). However, on older SIM cards, you can only store 1 number per contact. Most phones will make duplicates for a contact with each number if your copying from the phone memory to the SIM card. I've heard newer SIM cards don't have this limitation though.
As for the OP, it looks like she will have to go through and fix/add the contacts. When I got my Droid Eris, Verizon ****ed up the SIM import from my Nokia and it only had my contacts A through C (so, 12 out of 40 contacts and random duplicates).