Joel,
MSC stands for Mobile service Switching Center, i.e. an exchange for the mobile network.
The feature to hide your number at the called party is CLIR (Calling Line Identifier Restriction). You have to register this subscription with your service operator. And you may permanently enable it by using appropriate menu in your phone, or temporaryly use it by insert #31# before the phone number you are going to dial.
Brgds