I have the issue and I did the iphonedelivery fix from the Redmondpie post a few days ago. It seems to kill the unlock as the carrier selector is gone from the options menu, but it does alow you to send MMS.
Rebooting brings the unlock back, with no MMS. I am staying on ATT and only ran Ultrasn0w because I will be travelling to Mexico in a month and want to use a local SIM there. I just uninstalled the unlock and will reinstall it when I leave.