Iphone has bars, says sim not allowed?

Sprint said they unlocked my iphone, i did the back up, restore, and re installed my back up but i didn't get the message that said "you phone has been unlocked"
i put in a sim card with no mins and it said "searching" then said "no sim" so i out mins on it and now its getting service bars and 3G, but the iphone won't let me in because it says i need a sim from sprint. What do i do?

The phone isn't unlocked, and won't work until it is.

I really advise against going to carriers to unlock your phone. If you have a local phone shop, or even find a trustworthy service online, then you would be much better off like that.