We propose an argumentation-based agent model that supports service and partner selection in service-oriented computing settings. In this model, argumentation is also used to help agents resolve conflicts between themselves, whenever is required for the provision of services. The model relies upon an argumentation framework that is used in a modular architecture where Knowledge, Goals, Decisions and Priorities are manipulated by three specialized modules dealing with decision making, communication and negotiation. We formulate a distributed e-procurement process to illustrate how our agents select services and partners and can negotiate with one another.