In this work we describe an architecture supporting the exposition of Context-Aware services. First, we discuss the meaning of context in computing. Second, the data sources composing the context are listed and defined. A definition of the meaning of Context Aware service is also provided. Our design is based on these definitions, and targeted to provide Context-Aware services to mobile users. The key-feature of the architecture is the explicit orientation toward working in a condition where direct knowledge of the user state is minimal. Its power resides in the capability to infer the user context from indirect information. This feature is called Context-based Content Engine (CCE) and is designed to ease its integration with existing systems such as a typical telecom operator portal. Our service oriented design could be implemented by several programming framework. However we choose to adopt Java technology because of its wide diffusion among the telecom operators and we show the main details of our reference implementation