"Legacy telecommunications providers have spent a lot of marketing dollars on driving home the 'open source is bad' message," says Garrett Smith, director of marketing and business development at VoIP Supply. "Enterprises know that some of the public and the telecommunications community carry this world view and that their use of open-source telecommunications has the potential to cause 'damage.'"

Given the souring economy, hemorrhaging corporate bottom-lines and the panic in many a shareholder's eye, will this "as advertised" fear hold sway much longer?

Not bloody likely. "We're just seeing too many cases operating in open source for it not to go in the enterprise market," says Gerry Purdy, Ph.D., chief analyst of mobile and wireless at Frost & Sullivan.

Certainly, signs of an upcoming wave of open-source telephony adoption in the enterprise market are everywhere.

In fixed telephony, open-source projects are spreading like wildfire, the majority of them in VoIP form rushing to replace the expensive and restrictive PBX systems. Most such projects are powered by or built upon Digium's Asterisk, the world's largest open-source telephony project, with 1.5 million downloads in 2008.

"Asterisk is free. We require no registration or anything so there is no concrete data on who's using Asterisk; but based on forums and other communications, my suspicion is that every Fortune 100 company is testing or using Asterisk in some way," says John Todd, open source community director at Digium.

Asterisk allows deployers to build new telephone systems or to gradually migrate existing systems to new technologies by blending traditional and VoIP services. Several members of the Asterisk community have reversed-engineered proprietary VoIP protocols by Cisco, Nortel and others, so that companies' existing (and expensive) phone sets and hardware work with Asterisk-based telephony projects. Such projects are then easily customizable so that phone calls and company data can merge to fingertip usefulness.

One pioneer in the open-source telephony space is Fonality which in 2008 recorded a record 3.3 million open-source commercial installations. "But the truth is that open source is only the first layer of our overall solution," explains Chris Lyman, Fonality's CEO. "We started with an [open-source] stack, using components such as Linux, Asterisk, Apache and Perl. But, on top of that, we layered 5 million lines of our own proprietary code."

"Because of the muddying waters, we have started to use the word 'open source-based' to be a more accurate description of what we and so many companies now do," he added.

Indeed, hybrid and blended solutions are beginning to emerge as a strong trend swell. It's also becoming more difficult to determine where one telephony open-source project ends and another begins.

"SIP [Session Initiation Protocol] and other key standard compatibility is already there in the Asterisk code, so the mobile phone compatibility component already exists. A mobile phone can easily be an extension of the office system," explains Todd.

The mobile front itself is immersed in a sea change of open-source adoption. Among those changes are:

• Funambol's mobile synchronization server and development platform for mobile applications which renders Blackberry-esque capabilities on commodity handsets.

• Nokia's recent outright purchase of Symbian and its subsequent pledge to take the operating system open-source. The Nokia Symbian Foundation says it already has RIM-like capabilities to compete successfully for Blackberry users.

• LiMo, the Linux-based mobile organization, is building for towards enterprise mobile phone use. It isn't open-source yet, but given that LiMO is Linux, the prevailing expectation is that it will be open-source soon.

• Palm's PRE uses a Linux-based operating system called WebOS, which makes use of CSS, XHTML and JavaScript for broad compatibility with many applications.

• Google's Android has a true open-source operating system for mobile devices and competes with Microsoft, Symbian and Qualcomm.

It previously could be argued that handset movement toward open source could amount to nothing in the end, given U.S. carriers' ironclad hold on which handsets and features actually make it to users' hands. But that argument dissolves in the face of Verizon's recent bid to open its cellular network to compatible and certified devices. That play potentially breaks the locked device environment permanently. "If Android gets certified on the Verizon network, any phone that runs Android could complete calls on Verizon," says Gary Zimmerman, director of product marketing at Avotus. "So the switch between carriers no longer requires a swap of equipment."

This disconnection from the previously heavily-guarded and closed domains of carriers denotes a major and important shift. In essence, the opening of carriers' systems enables enterprises to achieve true unified communications: The holy grail of all things corporate.

But that is not to say that mobile open source is ready for activate-and-play corporate use.