MTN BIS FOR BB,From 1500 to 1000

I just loaded 1500 mtn recharge Card to do my BIS to my greatest supprise mtn took only 1000naira.
HOW TO DO MTN 1 MONTH BIS
Simply text Bbc to 21600. Instead of 1,500 is now 1000 naira.
Note: for Blackberry users only