This Trick is Only for Mtn Users Only ...
MTN gives u #500 bonus for #100 call but on MTN ZONE,you can make up to #100 call with just #5
from 12:00am to 5:00am
HOW DOES THE TRICK WORK?
Firstly, dial *507# to activate the bonus. Make sure u have at least #4 and at most #6
Then make call from after 12:00am till ur airtime get exhausted and u wil get #500 bonus to make calls for the day.
Tested and confirmed.
Source from
http://nairaclass.com/forum/index.php?topic=1106.msg1142;topicseen#msg1142