Can all mobile phones be unlocked?

Yeah, the majority of phones can be unlocked but there are a few exceptions. There are too many to mention individually, but the typical examples of this, include operator-exclusive phone models.

A good way to figure out whether your phone can be unlocked is by phoning your operator. In some cases, your operator won't be able to unlock your mobile, yet a professional high street unlocker will. Pop down the road and talk to your local unlocking shop for a near-definitive answer.