Caller ID is a great thing in many instances, as it lets you know who is calling so you can determine if you should answer or call them back later. In some instances, though, you may not want to have your number revealed to the person you are calling, as this is a way of protecting your privacy. While most phones allow you to make your number "private," not all cell phone providers allow you to use this service. Fortunately, you can block your cell phone number as private on T-Mobile.
Turn on your cell phone.
Press "Menu" and then select "Settings" (this may be called "Options" on some phone models).
Select "Call Settings" and then "Additional Call Settings" (this may be called "Advanced Settings" on some phone models).
Choose "Caller ID" and then select "Hide Number" ("Make Private" on some models). Save your changes and you are done.
If you only want to block your number for certain calls, dial 67 before the number. This will block your number from showing for that call only. Test it by dialling your own number with 67 before it and you will see if it works on your phone. If it does not, *1167 is the alternate code.
Remember that the same way you may decide not to answer calls which block their number, other people do the same and may not answer your calls with the number hidden. Decide when to make your number hidden to make sure that your calls are always taken.