here is how to get unlimited airtime from mtn
don't know if this is a promo but since sharing is caring. I going to share it with u guys.
simple dial *555*000012345612# then send and wait for response. keep changing the last eight digits to get more airtime. if you get service timed out or invalid pin don't give up generate new ones and try. remember do not change the 0000 after the second *