How to unlock sim on iphone 4 that was reset?

I just reset my iphone 4s and it locked my sim card. It says to plug it into itunes but it won't work and it says that i need to unlock my sim but it won't come up in my iphone screen.

Seems your phone is locked and the only method to make the activation work is unlock it first. The factory unlock depends on the network your phone is locked, and the price of the unlock depends on the network also. If you have said the network would have been able to give mode details about it. If do not know the network that can be found from your imei, normally for a cheap price from a specialized site, and based on that can see how much your unlock will be. Also can use a gevey sim or R-sim as an alternative to unlock your phone