If you call the phone's service provider (suncom?) and tell them you want to transfer the numbers from that phone to your "new" phone via the "new" sim card they should give you the unlock code. They don't like to give it out, but eventually someone will give it to you. I just finished doing this for a buddy of mine who got a verizon blackberry and wanted to transfer the numbers from his old ATT phone. We called ATT and they gave us the unlock code. FYI: Subsidy unlock codes (the ones that will unlock the phone for use with any provider) are unit specific. You'll need the IMEI or ESN number from under the battery of the phone.

Default is 1234 give that a try