Recently a friend asked me if it was possible to block sending his caller ID when he uses his mobile phone for all calls in general but define exceptions for calls to friends and family. Sounds complicated but it's actually rather simple. Here's how it can be done with any GSM or UMTS phone: First find the menu entry which lets you select if by default your caller ID is shown or not. For the scenario above, set it to “never show my caller ID” or similar. For your friends that should see your number when you call, go to the phone's phonebook select the relevant entries and add the following code in front of the phone number:
This tells the phone to inform the network not to apply caller ID blocking for this call. It's a standardized GSM/UMTS supplementary service code so it should work with pretty much any phone. For more of those codes have a look here.