Nowhere near 20% huh?
http://en.wikipedia.org/wiki/M-Pesa#Cost.2C_transaction_charges.2C_statisticsThe transaction charges range is from 66% down to 0.16% depending who is involved and the amount of money:
up to 66% for a transfer to an unregistered user
up to 30% for a transfer to a registered user
the lowest transfer rate is 0.16% to a registered user for KSH 70'000 (800 USD, 580 EUR)
the cost for withdrawing money from an M-Pesa agent reach from 20% max to min 0.47%
Look at the lower rates (0.16%) - between registered users. That is what most people pay. Pretty cheap compared to the volatility risk of BTC + exchange commisions.