Reliability is the most critical aspect of a business phone system. IP telephony systems will deliver differing service levels because their architecture is fundamentally different. Ironically, optimal architecture and design does not only deliver high reliability, but also produces a system that is easy to use and manage.

This whitepaper,""Building Reliable IP Telephony Systems"" defines reliability & availability and compares various IP telephony vendors and how they ensure high availability. System design and architecture dictate the type of redundancy that can be deployed to increase reliability.