Wherever you bought the phone, you should be able to take in your old phone and they can move transfer your contacts from the old sim card to the iPhone sim card.
The only way that I have seen to do it at home is with a Jailbroken iPhone, there are programs which will sync your contacts from the old sim to the phone. But, I would suggest taking it to the store. It's much easier.
If you'd like to jailbreak, go to the Jailbroken forums here at TiPb and read up on the guide they have.
OK I got it to work. I swapped the SIM from my RAZR and imported the contacts. The contacts need to be cleaned up a bit but it worked. I just needed to put the SIM in a couple of times till it was recognized by the iphone