This list of GSM codes for mobile phones that use GSM includes some great information for controlling many service settings. Many phones allow you to globally enable or disable outgoing caller ID, but most do not allow you to disable outgoing caller ID per call made.

If you have outgoing caller ID enabled like most people do, you can dial #31#number (#31# for the prefix of any phone number) and it will block your outgoing caller ID and say Private on the receiving end for that one call. Another useful set of GSM codes are for setting call forwarding.

Instead of using the phone menu system for setting call fowarding, you can use **21*number[SEND] to activate call forwarding to a specific number, and then use ##21#[SEND] to cancel call forwarding. Using these call forwarding GSM codes, you can set speed dial numbers for setting and canceling call forwarding quickly rather than using the phone menu system. These are just a few examples of how you can use GSM codes directly with your GSM phone.