VoIP is finally becoming a mainstream application for small and large business -- but with IP telephony at the high end, and Skype cleaning up in homes and home offices, there's a gap in the market.

If your connectivity is based on Frame Relay or metro Ethernet, you're most likely a big enterprise with hundreds if not thousands of employees on several sites, and you use probably those connections to provide Internet access, as well as inter-office or branch office connectivity.

Small businesses on the other hand can get away with the kinds of systems sold by BT and Vonage. Both sell systems consisting of an adapter box that does the translation work required to make a handful of SIP phones work over a broadband connection -- often ADSL or, increasingly, SDSL.

For enterprises in between these two extremes, neither of these models is suitable. It's this area that SIPFoundry and its PingTel commercial arm are exploring -- the aim is to bring the advantages of open source VoIP software to the SIP phone market for medium-sized enterprises.

SIPFoundry is an international open-source community which acts as an umbrella group to accelerate the adoption of SIP. According to board member Martin Steinmann, the organisation aims to commoditise the technology, make it ubiquitous, and make multimedia -- including SIP applications of course -- easy, simple, and network- and hardware-independent.

The body has just announced two new software modules: repro, a SIP proxy server designed to add IETF-developed security features to carriers' SIP-enabled networks; and sipXtapi, and a SIP user agent for Linux and Windows. The agent adds an API which simplifies the development of softphones and similar clients.

These build on existing SIPFoundry software such as its open source Linux PBX and its two end user applications: the sipXphone softphone and the tongue-twisting user agent sipXezPhone.

PingTel acts as the commercial side of the relationship. Its plans include "becoming the equivalent of Red Hat in the SIP arena", according to president and CEO Bill Rich. It is repackaging SIPFoundry's software for SIP PBXs, converting source code into the appropriate binaries, and adding support, quality control, guarantees, management tools, 24/7 technology support, marketing, documentation and so on.

The key benefit according to Rich is that from an enterprise point of view, there's less risk involved in buying systems based on open standards. He says a standards-based SIP phone will just work, unlike systems from major players such as Siemens, Avaya, and Nortel.

PingTel is in the throes of moving aggressively into the European market, primarily by building relationships with European distributors. It has just announced relationships with six channel partners and two so-called ecosystem partners. The latters' role is to provide the infrastructure that will enable PingTel's solutions to work, especially the gateways that move Internet voice traffic onto the public switch telephone network (PSTN).

With few non-proprietary products available for the medium-sized business, PingTel aims to sell complete packages through its resellers that will allow organisations to replace their costly PSTN-based PBXes with near-free open source equivalents, adding free phone calls along the way in exchange for various forms of monthly subscription.

Its core offering is the SIPxchange PBX, which provides services such as call management and softphone applications.

"Unlike Cisco etc we are standards-based", said Rich. "Our systems are sold by licence not seat. Avaya for example, sells by the seat, we sell an annual software subscription which buys you the right to support. The software runs on a standard Linux server. And we even support phones from others such as Cisco as long as they are SIP standards-based.

"We integrate databases and access to the PSTN -- key is the ability to integrate into users' contact databases," said Rich.

"The only drawback of the PingTel offering is that we don't yet have WiMax, and you [Europeans] don't have a naked [unbundled] DSL line, so you still have to pay BT for the line, which means you're still paying rental," he adds. "And customers still need to be educated that voice traffic will experience drop-outs when there are big downloads going on."

They also need to understand that it's not just about money, he says: "We focus on the 50 to 200 seat market, and are selling productivity not savings."