Unlocked Iphone 5 IOS 1.6.4 No Service Issue?

Since today i`ve been having this issue with my network signal, my phone used to display "Movistar" (my network carrier) but now it says no signal, it just happened randomly, and it doesnt get any signal.I have already restored network settings, removing the sim card and also i did a full reset but nothing, also i wanted to know if i can be something with my sim card, because since i bought it, sometimes my phone used to tell me that there was no sim card installed but i just reboot my phone and it made it work again, also when I go to settings and then to carrier it is able to find some carries, (my carrier is one of them.)

PD: my iphone recognises the sim card, but it isn`t able to get service.