So I just got a new prepaid plan (49.99 unlimited) and its saying no sim, can I even activate my new card using a iphone? or maybe I didn't cut it right? help please (got this sim like 2 hours and 30 min ago)

(Ultra snow installed and iOS4 MMS Fix)

I tried my friends tmobile card long ago and it worked fine so i don't know what the problem is :/