You can visit a mobile service centre and they should be able to reset the lock code for a small fee. Alternatively you could try entering the lock code incorrectly 3 times or until it asks for your PUK code. Once it asks for your PUK code, you can enter it and your lock code should be reseted to default settings (maybe 12345). This is the case with alot of Nokia phones, but it could erase your contacts. To be safe, you might be better off going using my first suggestion.

The wireless providers use either the SIM card number from GSM providers (Cingular and T-Mobile) or the ESN number on a device (Verizon and Sprint) to associate your wireless number. These numbers should never be given out to anyone except your provider (or authorized reseller). I can't imagine why a game company needs your IMEI number, except because they may put that into a database to associate you with the "license" he is providing to you. There is no way that he can track your IMEI since it is not sent through anything wirelessly. Personally, I would not send your actual IMEI. I would take a look at your IMEI on your device and then change the last three or four digits and send that to him. He won't know the difference, believe me. It's the first 5-7 digits or so that identify the type of device, so if you tell him you have a Motorola Razr, for example, and he knows anything about IMEI's, he will know that the Razr's IMEI starts with 3571234, for example (not real, just an example).

In this case, sending the IMEI number should be fine. The person needs it to prevent software piracy. Each phone has a unique number to identify it, so once the person has your IMEI number, the passcode will only work for your phone. Its just a safeguard to prevent you from passing the game onto someone else.

An IMEI number is also used to disable a phone, so for example your phone was stolen, if you were to contact your network provider quoting your IMEI number, they'll be able to disable the phone, so whoever has it wont be able to use it, even if they were to place their own sim card into it. Of course, I'm sure network providers ask security questions first to make sure you were the owner of the phone.

Your IMEI number is a unique number that identifies your phone. For example, if I had that number I could remotely hack into your phone and empty your credits.