Service-oriented architecture is an idea, not a technology. Boundless in scope, it promises both unlimited software reuse and the interconnection of everything, as long as IT is willing to wrap legacy applications in standard interfaces and construct new apps as services, the capabilities of which other software can tap into.
The idea is simple, but the execution isn't, because SOA turns the conventional model of enterprise software development on its head. Normally, programmers write software based on a set of well-defined requirements. SOA demands that organisations create an ecosystem of services that may ultimately have an army of stakeholders inside and outside the firewall. The initial challenge of SOA is knowing where and how to start -- where to draw a box around a fixed set of requirements and how to build services that will yield tangible ROI while keeping an SOA fully extensible.
Telecom providers are competing tooth and nail to provide consumer and business customers with the latest and greatest value-added services. This smorgasbord of offerings includes everything from ring-tone downloads to hosted messaging, accounting, and other business services. An SOA makes perfect sense in this have-it-your-way environment because it enables providers to cobble together new offerings with those of third parties and integrate them quickly with their internal, mainframe-based billing, provisioning, and other support systems.
