Manual mode (for a single call) Dial #31# before your contact's phone number.* Automatic mode (for all the calls) Open "Phone" app : - tap on, - tap on "Settings", - tap on "Calling accounts", - select a SIM card or an operator, if needed - tap on "GSM call settings", Settings" or "Additional settings", - tap on "Additional settings", if needed, - tap on "Caller ID", - select "Hide number".
NB : call number is not hidden for sending SMS/MMS.