Motorola SLVR L7

With an unbranded phone on Cingular network, i cant get my message icon to go away. I have tried to talk to cingular tech people, but no help has come from that. I tried a master reset. I tried cycling the phone on and off. The only way i can get it to go away, is if i put someone else's SIM in my phone and then switch back.
Anyone else have this issue?
Anyone else know how to solve it?
Thanks,
-Joe