African mobile phone operator Vodacom on Wednesday reported a 40-percent jump in revenue from data usage in the fourth quarter, as smart phone use continued to grow.

The Johannesburg-based firm—majority owned by Britain's Vodafone—said 7.2 million customers were using smartphones in its main market, South Africa, by the end of the year.

That was up 600,000 from the third quarter, with the average data used increasing 83.5 percent to 254 megabytes per month.

The average US customer uses about 1.4 gigabytes a month.

Vodacom's operations elsewhere in Africa—Mozambique, Nigeria, Lesotho, Tanzania and the Democratic Republic of Congo—also saw an increase in data customers, said CEO Shameel Joosub.

"Data revenue more than doubled with data traffic now three times higher than a year ago," he said.

That will be seen as good news for mobile phone companies who are banking on increased data revenue to offset a fall in cell phone calls.

The uptake of phones in rapidly growing Africa is also helping.

Last year a study found that roughly two-thirds of the sub-Saharan population were still without a .

But Vodacom's statistics showed just how much ground needs to be made up.

The firm, which boasts 56 million customers, reported that data made up around 22 percent of service revenue in the fourth quarter.