Apple Iphone 4 16GB on O2 ?

Used Iphone 4 on O2 but think it works on any network however not sure so buyer would have to check this phone is only 11 months old perfect working order has two tiny marks to top of phone but not really noticable has had front and rear screen protectors on from new comes complete with box handsfree headphones charger instructions etc only selling due to getting company phone