Considering the shift from physical to virtual goods, it's no surprise there's also been an explosion in the number of billing and payment options over the past couple of years.

UK outfit GoPayforit is the latest to offer more flexibility.

It's a mobile phone based system that has you entering your phone number and then receiving a texted pin number to confirm purchases of between 25p to £10.

It uses UK operators' billing systems so works with contract or Pay As You Go, and doesn't involve a bank account or premium SMS.

As well as being easy for users - you only have to enter 16 digits (although your phone does need a network connection) - the company says that online retailers - including game developers - only need to insert a single line of code to generate a purchasing button.

Payment terms are listed as being the 10th day of the following month, while payment rates depend on the different operators' charges.

However there are a couple of restrictions. At present, you can't use it for subscription services, and it's limited to users of UK networks, although the company is working on both of these.

For more details about GoPayforit, check out its website.