In this Clear Choice test of four open source-based IP PBX systems, we found products that are well suited for the low end -- defined in this testing as supporting as many as 250 concurrent users. By providing simple installation processes, automatic endpoint configuration and straightforward Web-based management interfaces, these products could go a long way in easing IT fears about dealing with open source VOIP products.

While this initial test of these products focused on smaller-scale deployment models, several of the systems tested also lend themselves to larger deployments. They incorporate more-advanced features, such as standby systems for failover and user presence capabilities. All provide full Session Initiation Protocol (SIP) support for endpoints as well as trunks. The management interfaces are simple but also provide detail for troubleshooting and bandwidth control necessary in larger environments.

The vendors that accepted our invitation were Escaux, Fonality, Four Loop Technologies and Pingtel. All four products were built on top of Asterisk, the original open source IP PBX (see the assessment of Digium's Asterisk offering below). The four vendors in our test demonstrated tangible improvements to existing open source IP PBX base code, especially in their efforts to facilitate installation, management and maintenance with GUIs.

The systems were ordered and provisioned as a customer would procure them. We then put them through their paces looking at management, features, interoperability, ease of use and architecture. Because performance metrics such as voice quality are dependent on the endpoint chosen, it was not a key factor in this test.

Pingtel's SIPxchange earns the Clear Choice award for triumphing over the field in our endpoint interoperability and architecture categories. In the latter category we examined how the product was designed to work. SIPxchange comprises some of the more common practices found in larger, proprietary systems, such as direct paths for the media streams. This limits the burden on the server and allows for better scalability and reliability. Also garnering respectably high scores in our tests were Four Loop and Fonality, but these companies earned their kudos for different reasons. Four Loop's Switchvox has advanced features -- such as a built-in switchboard -- that were better than most. Fonality's PBXtra was the leader of the pack in terms of ease of use, mainly because standard support includes off-site monitoring and management services.

Here is a product-by-product breakdown of our complete test results.