An open source group has posted free PBX software that lets businesses create their own phone switches from standard Linux servers - but drawing business customers to the technology could be an uphill effort.

Called sipX, the PBX offering is compatible with SIP phones and media gateways that can change IP voice to traditional TDM voice and vice versa so calls can be switched onto traditional phone networks.

SipX was written by SIPFoundry, whose goal is to encourage businesses to develop interoperable SIP products so end users can readily take advantage of SIP features, such as presence, without tweaking the equipment they use. The organisation considers itself a developer community where members can contribute to writing open source code, similar to the Linux development community.

Development of sipX parallels similar efforts that produced Asterisk free PBX software, backed by equipment vendor Digium. Asterisk was released last September.

While free software might be attractive to some, it is unlikely to become a major force in large businesses. "It has potential for small organisations or homes, but it's unlikely to make a significant dent in the enterprise," where customers want more than just a PBX, says Paul Strauss, a research manager at IDC. "You do need support; you do want assurances of quality. You do need to see what's going on inside it; you want the vendor to sell you phones."

SIPFoundry's key founder, PingTel Corp., says it hopes that businesses interested in the open-source SIP software will buy it along with supplemental software tools and support from PingTel, using the same model Red Hat uses with Linux. PingTel sells PBX support services wrapped around a version of sipX.

PingTel's share of the IP PBX market is too small to count, Strauss says. According to IDC, IP PBX technology is driven not by traditional circuit-switched PBX vendors but by new vendors, and that doesn't mean start-ups. 3Com and Cisco, which have quickly dominated corporate IP voice, are considered new vendors because they only leapt into PBX sales with IP offerings. Avaya, Nortel, Siemens, NEC and Toshiba - the traditional PBX leaders - have all revamped their offerings to include IP.