If your phone is stolen, make sure nobody can use it by simply blocking it. If the phone is blocked nobody can use it and chances are the person who robbed it could send it back to you.
# You will need you 15 digit IMEI number. If it's 17 digits you need only the first 15 digits.
#* IMEI number can be found by typing *#06# on your phone.
#*If you don't have the phone on you, check the phone manual, box or the receipt. Chances are the number might be printed on the label somewhere!
# Call the service provider to block it temporarily. Make sure not to block it permanently because you can still find it.
* If you get it back call the service provider to unlock it.