Unlocked my iphone from o2 but meteor sim card won't work?

I unlocked my iphone from o2 the other day and it gave me instructions on how to set up the new sim card via itunes. I followed them but even though the phone says meteor in the top left corner of the screen it won't give me any bars for signal. Any ideas what could be the problem?

If the phone is accepting the SIM then it will be unlocked, so the problem is either with the SIM or with the phone picking up a signal.

Firstly, put the SIM in another phone to see if you can get a signal and make a call/text. If it works ok, then you know the problem is with the iPhone. If the SIM also does not work in another phone then you'll need to call Meteor to get them to check out the SIM.

If the SIM works fine in another phone, put it back in the iPhone and perform a hard reboot on an iPhone by holding down the home button and the top 'lock' button at the same time for about 20 seconds until you see an Apple logo on the screen, then release the buttons.
This reboots the phones software without deleting any data or settings and helps to clear any temporary software glitches.

Then try again, if it still doesn't work then try to reset the network settings by going to Settings > General > Reset > Reset Network Settings.

If after trying all of this and it still doesn't work then you may need to take the phone to an Apple store for a guru to take a look at it for you.