Can the Samsung SGH-X426 be unlocked?

Not sure the significance of these numbers: Rev. 1.6 X46UEDC1
After Typing in code 1 followed by the IMEI. I am getting a Wrong Entry Message. I am trying to use my old Samsung (AT&T wireless) phone which originally came with an AT&T SIM card. I broke my new phone which uses a Cingular SIM card, but Wrong Card pops up when I put the Cingular/AT&T SIM card in my old phone. Can this even be done? PLEASE HELP!!!

I am a tec at Mobile One Wireless in Madison Wisconsin and we have a ns pro box that we can unlock a samsung for you.