SIM card is "UNREGISTERED" when it shouldn't be! pls help!?

I just got this SIM card put in the phone not even 3 hours ago & it usually takes an hour for it to kick in (as in fully functional calls/texts etc.) but for some reason it just says that the SIM unregistered & wont allow me to call anyone except for emergency calls! this is veery important I'm the kind of person who just CANT live without my phone so the sooner someone replies the better! its a Samsung Galaxy S phone brand new, has never been dropped or anything for it to be doing this.. I paid $45 at a local phone genius lol who has set up this same exact phone for us before with absolutely no problems.. but if you know ANYTHING, anything at all that you think would help me with this dilemma I'm experiencing (a little dramatic! lol) I would appreciate it veery much and will give points to the person with the best answer!