Call to all networks in Nigeria are charged at N0.11 per second from the very first second for a daily access fee of N5.00 charged on your first call of the day.
Let's assumed you recharge N100 / Day:
* Daily "Access fee" = N5.00 (e.i. N100.00 - N5.00 = N95.00 balance).
* N0.11 / second (e.i. N 6.60 / minute) - to all networks.
Therefor, with N100 Airtel airtime/recharge card, you will make calls for 14 minutes, 39 seconds (N95.00 / N6.60).