Need help with new iPhone

[Fisher_D]

So last may I got the lg vu, but then my family got a first gen iphone around december and I switched over to that and registered. This July, the phone dropped and it cracked and so I switched back to my vu. Today I bought a used iPhone and I put my sim card in, but it won't register it. I've tried plugging it in to the computer but it says it needs to be put a sim card in and I've tried plugging it in again and again and I've took it out and put it back in but nothing works. It still works and registers in my vu and I've tried putting it back in my old iPhone and it still registers it. Is there any way to get it to register? like do I have to jail break it or anything or is the only way to get it working is to get a new sim card? Any help would be much appreciated!

[Napoleon_PhoneApart]

It sounds as if your iPhone isn't unlocked to work on non-AT&T carriers. You need an iPhone sim to put in your new iPhone.

[Kuntry]

I'm not 100% positive, but I think the Vu is AT&T exclusive. Fisher, are you with AT&T? If you are, is it already jailbroken? If so, go to Cydia and see if Ultrasn0w is installed. If it is, uninstall it (if you're on AT&T) and reboot your phone with the SIM card in it (you may have to reboot more than once).

If you aren't jailbroken already, I would suggest stopping by an AT&T store and try getting a new SIM card. If you want to save a couple bucks, try calling AT&T customer service first and tell them your having a problem with your SIM registering in your device and ask if they will replace the SIM for free. If they agree (most likely they will) they will note the free SIM in your account and then you can go to an AT&T store and pick it up, free of charge.