In recent years, many Mobile Payment (MP) schemes have been proposed and used in practise. However, a prerequisite for extended acceptance and adoption of MP technologies is to deploy an effective MP system. So far, there is no such a standardised and scalable MP platform. Most current MP schemes are circumscribed by its mobile network infrastructures.??Fortunately, the fast advancement of 3G technology equips next generation mobile phone network more benefits. Following this direction, we propose SIMPA --- A SIP-based Mobile Payment Architecture for next generation mobile network, which not only supports P2P payment communications between customers and merchants using Session Initiation Protocol (SIP), but also supports several traditional internet security protocols, to enhance privacy, confidentiality and integrity during the transaction. This paper depicts detailed protocol and system architecture of SIMPA. Some application examples from customers’ view are shown to demonstrate its function and feature.