To 28-year-old Kenyan Mary Wanjiku, her cell phone is not just a cell phone. It is also a cheap, safe and easy way of sending her mother $40.

But by using it to ping cash to friends and family she and millions of Africans are joining Japan in breaking a technology barrier that remains in Europe and the United States, and paving the way to what could be the cash of the future.

"Before, I would be forced to make the journey home to deliver the money," Ms Wanjiku said outside a Nairobi shop that doubles as an agent for M-PESA, the virtual cash network that means "mobile money" in Swahili, Kenya's lingua franca.

"M-PESA has revolutionised my life."

The network, owned by Kenya's biggest mobile phone firm Safaricom, has its roots in Africa's lack of infrastructure - particularly bank branches - and the enthusiasm with which people have taken to mobile phones.

Only one in five people have bank accounts, mainly because of the prohibitive cost to the banks of operating branches in far-flung parts of a continent where many of the population of one billion live on a few dollars a day or less.

But mobile phones are spreading extremely fast: to 270 million in 2007 from just 50 million in 2003, according to industry association GSMA.

Teaming up with Kenya Commercial Bank to let phone users who do not have bank accounts send each other money, M-PESA hit on a formula that has attracted 6.5 million customers, or one in six Kenyans, in just over two years.

In Japan, which has pioneered the technology and business models toward wallet phones, about 55 million mobile phones have an e-money function, so about half of Japanese users carry them.

The global market for mobile money is growing at 70 per cent a year and should attain "mainstream" status by 2012 with more than 190 million customers, or more than three percent of mobile users, IT consultancy Gartner said in a May report.