Mobile phone use in the developing world is skyrocketing. With costs as low as $10 per phone, more than half of the population living in the developing world are now cell phone subscribers.

It's no surprise, then, to see our clients doing business on their mobile phones. In fact, for many of our clients their cell phone is their business - they use an Opportunity loan to purchase minutes in bulk and then rent use of their phone to neighbours.

Cell phones also present a natural, cost-effective way to expand microfinance to those who need it most. Opportunity's new mobile banking services in Malawi and Kenya allow clients to make loan repayments or transfer funds into Opportunity savings accounts by phone. They can also check account balances, transfer money between accounts, pay bills, receive salary or government payments, and buy airtime.

As Opportunity's Dennis Ripley observes, mobile payments make it possible for individuals to save as little as $1 or $2 at a time - amounts too small for deposits to formal banks, given the 30 cent cost of a deposit. It can therefore be the first step into the formal financial system for the unbanked. Read Dennis' interview.

One anticipated roadblock to the expansion of mobile banking is the availability of electricity to recharge the phones. In an interview with the Financial Times, Aleksandr-Alain Kalanda, chief executive of Opportunity Malawi, says this hurdle can be overcome by "increasing use of solar chargers, with neighbours or farmers working together in co-operatives, sharing the cost of the technology."