MTN free call to all networks at its best
Steps to Follow:
1: get two (2) MTN extra cool sim (sim A and sim B)
2: make sure you have #100 on both sim but don't be afraid they won't touch your money
3: divert all sim A call to sim B
4: keep your sim A and put only sim B after that you are good to make free MTN call to all network.
It works fine and it's free MTN Nigeria call.