With the growth of information content accessible by web, peer-to-peer and mobile devices, new approaches to large volume, small value payment are needed. We describe the NetPay micro-payment protocol that we have extended from its original pay-per-click for web content to peer-to-peer networks and mobile device networks.We outline the keymotivation for NetPay, the basic micro-payment protocol using e-coins and e-wallets, and our three variants of the protocol for different domains. We conclude with a discussion of our prototype implementations and evaluations of the NetPay protocol to date.