If you are unsure of the warranty status or the network the iphone 2g 3g 3gs or iphone 4 was sold on.

Factory unlock code for iphones where unlock via itunes can be done need the info of the network.

Simply download the software from here

http://rebelsimcard.com/Rebel_iPhone_network_checker.rar

enter username and password we supply after payment
you can check 1 phone and see its status in realtime

The service takes 2 credits and the user and pass info has 2 credits on it so you can perform 1 check

Checking with server...
Verifying
You have 2 credits left
Done.
Checking with server...
Verifying
Processing...
Requesting info
Info:
iPhone 4 16GB Black (4.2.1)
IMEI: 01xxxxxxxxxxxxx
Serial number: 7W049210A4S
Limited Warranty: 2011-01-16 / 2012-01-15
Sold to country: United Kingdom
Carrier: Orange GBR

Now you will know the network the iphone is locked on to in seconds.