The strong growth in the use of debit cards as a preferred payment method will be challenged by the New Payments Platform, the low-value payments infrastructure planned for the Australian financial system.The NPP, whose development is being administered by the Australian Payments Clearing Association, is intended to be fast and flexible, allowing real-time settlements. It will also be able to support a host of innovative "overlays".One overlay that was the subject of discussion at last week's CeBIT Future of Payments conference in Sydney was a mobile payment service that bypasses all the established card schemes.Jim Mortimer, the head of international propositions at the UK payment systems' developer VocaLink, said application-based systems that allowed the consumer to make payments to personal or business mobile numbers were achieving a level of bank-to-bank interoperability that could challenge debit card issuers.An example of this type of service is Barclays Bank's Pingit, which works regardless of whether the parties are Barclays customers or not.Services such as Pingit rely on a piece of payments infrastructure called the Faster Payments Service, which was launched in 2008 and is a model for Australia's NPP.Westpac Institutional Bank's head of payments, Philip Joyce, said: "The UK experience shows us that there are value propositions that will challenge debit."Australian Payments Clearing Association's chief executive, Chris Hamilton, said the UK's Payments Council was developing a mobile phone addressing standard. This would facilitate mobile technology as an alternative payment scheme using a fast payment network.Hamilton said such a service was a good example of the sort of overlay that could be introduced to the NPP system when it was up and running.In the meantime, consumers are continuing to increase their use of debit cards in preference to credit cards. MWE Consulting's analysis of the latest Reserve Bank card statistics, released yesterday, shows that debit made up 41.7 per cent of the value of card purchases in August - up from 40.1 per cent in August last year.According to MWE, 47.4 per cent of the value of card payments are made on credit cards - down from 48.3 per cent a year earlier. And 10.9 per cent of card payments are made on charge cards - down from 11.6 per cent a year earlier.When it comes to the number of transactions, debit is way out in front. Debit made up 63.7 per cent of card purchases in August, compared with 33.2 per cent for credit cards and 3.1 per cent for charge cards.