This paper describes the system architecture for a terminal-based location service enabler in the 3rd generation (3G) IP multimedia subsystem (IMS). A location service enabler provides data about the geographical position of mobile terminals to requesting clients. Since location data can be regarded as a type of presence information, we propose an architecture that builds on the IMS presence specifications. We show that several mechanisms for processing presence like notification handling, access control and privacy management apply to location data as well. It is therefore possible to reuse a large part of the IMS presence infrastructure. Based on the observation that the processing of trigger conditions for location information and creating notification messages should be done in the terminal itself, we propose a terminal-based location enabler. The terminal uses a built-in method to determine its geographical position such as a Global Positioning System (GPS) module. We argue that the proposed architecture scales better and is more accurate, efficient and cost effective than current network-based location enablers