Did you enable the parameter “ATT” that allows a MS to perform an IMSI Attach ?
Otherwise the phone is ON, but not attached.
Second possibility: the MS was detached too early. Check that you T DETACH in the VLR (NSS parameter) is 2x greater (and a little more) than your T3212.
T_Detach = (2 x T3212)+20mn for example.