I am seeing exactly the same symptoms as you except i did my JB and UL quite a while ago and was working on a T-Mobile SIM until today. Now only ATT SIM works, T-Mobile SIM gives "Invalid SIM" at the top where Carrier is normally displayed and a pop up message saying SIM failure.
I deleted and re-installed ultrasn0w, Tried the hactivation patch in Pushfix on Cydia, restarted the phone, airplane on and off. Nothing seem to work. I have a Samsung Quad-band Unlocked phone in which all my SIMS worked. Only thing left to do is a restore but will leave that until tomorrow because Cydia seems a bit flaky today.