hi guys. i have a bit of a problem here. so here are the details.

a few months a go when i was in the us i bought a couple of iphones and brought them to my country which is iran.now all of the iphones are working except one. well actually everything works i can recive and give sms and i can go in the internet but the only thing that doesnt work is that i cant call any1. i can recive calls but i can’t give any. and it is not because of my sim because i have tried it with other peoples sims. PLEASE HELP. oh by the way my i phone is unlocked but thats not the problem since all the others work and i unlocked them in the same way