you could, you will need the carriers Mip/SIP settings, prl, imsi. sid, and carrier code. the only problem is as of now the RSD's dont have the matrix file to change or manipulate that information, you could get risky and use Qpst. I'm 100 Percent you could get it to make calls, 25-50% Data.
Could you please elaborate, I thought the Droid X was locked and that without cracking the bootloader a true unlock would be impossible.
If this other carrier is CDMA, unlocking is not the problem, you can force a phone to roam on any network if you wanted it to. The work is trying to get it to A. Do the over the air activation. B. trying to get the phone to recognize that carriers data settings to use it on their network.
The first major hurdle is if the other carrier has that phone in their device database, if not, if there is a generic ESN Database entry for smartphones.
If the other carrier is GSM, then you are out of luck.
If you can get me the carrier name, I can give you the details for the radio setup.