Iphone 4 - The SIM card in this Iphone does not appear to be supported?

My dad gave me a new iphone, but when i put in my O2 micro sim it just came up with this…
The model number is - A1332
does anyone know what the carrier its lock to is?

Almost All iPhones Auto-lock to the 1st SIM that is put it them
before that, they are not locked to any network.
Very very few are unlocked ones.

The model number does not tell you which network it is for.
The apple Genius bar can, if you call the apple shop/support line

You could also go look at the Settings->General->Network or About menus
it may also show the locked network there.