In services oriented computing, location or spatial models are required to model the domain environment whenever location or spatial relationships are utilised by users and/or services. This research presents an ontology-based methodology for context-aware messaging service. There are five main contributions to this research. First, the research provides a service oriented methodology for modelling and building contextaware messaging systems based on ontological principles. Second, it describes a method that assists understanding the domain's spatial environment. Third, it includes a proposal of the generic Mona-ServOnt core service ontology that offers context-aware reasoning for capture and use of context. Mona-ServOnt is able to support the deployment of context-aware messaging services in both indoor and outdoor environments. Fourth, a novel generic architecture that captures the requirements for context-aware messaging services is given. Fifth, the generic messaging protocols that describe the exchange of messages within context-aware messaging services is modelled. A few experiments were completed to measure the performance of the peer-to-peer services using actual smartphone with Bluetooth capability. In addition, the methodology's main steps have been validated individually in various context-aware messaging domains. It has been evaluated using competency questions that gauge the scope of the proposed ontology. Furthermore, the generic architecture and messaging protocols have been verified in constructing for each domain.