Every phone has some secret functions that can be unlocked; and almost none of them are of any interest to the average user. Most unlocked features do such things as display network identification codes, date of manufacture, date of last repair, software versions, and so on.
Caution: Messing with your phone and trying to unlock hidden features could render it useless and violate terms of your contract with your cell carrier. It really isn't worth the trouble; especially since any cool customization that you'll want to do (graphics, ring tones) can be done without unlocking anything.
There are one or two handsets that have hidden games, usually hidden within other games installed on the phone. An Internet search will reveal if your model of phone has any hidden games and how to unlock them. These are generally limited to some Ericsson and Nokia handsets.
Gaming on your mobile device:
There are several Web sites that offer game software for your mobile phone. Although gaming capabilities vary from phone to phone, newer models, like the Nokia N-Gage, feature games that rival some Game Boy titles. The trend of gaming on cell phones (dubbed casual gaming) is growing quickly as more game developers and better games appear all the time.
Unlike desktop and console games that can be extremely complicated and have a long learning curve, most mobile games are almost intuitive. They may take only a moment to learn and a few minutes to play. The limitations of mobile devices have led developers to be creative and create simple games that are entertaining and addictive.
In most cases, you will only be charged airtime when downloading a game, not when you are playing it. The exception to this is if you are playing a multiplayer game over your carrier's network, or a game that requires you to interact with a game server, like a WAP game.
If you're an avid gamer, remember that gaming can be a drain on your phone's battery. Games utilize the phone's processor and display more than placing a call does; and they are more than a little addictive, so you can quickly find yourself spending hours playing them.