San Francisco-based start-up Boku has launched a mobile payment service that enables users to buy virtual goods offered on online games and social networks by submitting their phone number instead of credit card details. The charge is then included in the next phone bill.

Boku claims this is both more convenient and opens up the market to the many millions of people who don’t have a credit card: the market for virtual goods and online gaming is worth $8 billion worldwide and is growing, according to Boku and, there are twice as many mobile phones as bank accounts – 4 billion versus 2 billion.

Boku said it has signed up 170 carriers in 50 countries to accept payments via its system. The company has raised $13 million in venture funding led by Benchmark Capital, with participation from Index Ventures and Khosla Ventures.

Yesterday Boku also announced it had acquired two privately held mobile payment companies, Paymo and Mobillcash. Financial details were not disclosed.