Picking 25 established unified communications and VoIP providers the IT channel absolutely, positively needs to know? It's hardly an exact science. You'll notice that we have focused our attention more on those vendors with on-premises offerings and from the more traditional IP-PBX and VoIP equipment worlds than telecom, as-a-service and cloud providers, with full understanding that the lines between what constitutes an IT networking vendor in the UC/VoIP arena and what constitutes a UC/VoIP service provider are blurrier than ever.

Here's a look, in alphabetical order.

Channel Chief: John Drolet

With a full range of SMB and enterprise-level IP communications products, Aastra has been an up-and-comer for some time, a status many trace to its 2008 acquisition of Ericsson’s enterprise PBX business.

Channel Chief: Ted Cole

Mighty Adtran, beloved by many in the channel for its airtight partner program, formally entered the UC market in December 2009 with the launch of four product lines in its NetVanta UC portfolio.

Channel Chief: Mike Moors

Partner programs haven’t always been Alcatel-Lucent’s strong suit, but its loyal solution providers swear by its products, which include the Omni-Touch 8400 Instant Communications Suite.

Channel Chief: Jeremy Butt

Thanks to its acquisition of Nortel’s former enterprise unit, Avaya, by most analyst estimations, commands about 25% of the global PBX market. But it’s been a strong and powerful UC player for some time.

Channel Chief: Bryan Kennedy

Avistar in 2007 went live with a worldwide reseller program to grab share outside financial services. With 15-plus years in desktop videoconferencing, its prime products include its C3 line.

Channel Chief: Edison Peres

Cisco entered the voice market more than a decade ago and the rest is history: It’s a networking powerhouse, a VoIP and UC powerhouse, a powerhouse, period. Key to continuing this was its acquisition of Tandberg, which vaulted it to the No. 1 market share among enterprise videoconferencing vendors.

Channel Chief: Stephen DiEugenio

If audioconferencing and collaboration are the topic, you include ClearOne, which has been serving it up for 20 years and has more than half of global market share in professional audioconferencing, specializing in both analog and VoIP settings.

Among its recent industry wins were a Frost & Sullivan award for market share leadership in the installed audio conferencing endpoints market.

Channel Chief: Steve Harvey

As the barriers to opensource PBX adoption came down, Digium took up the mantle as the scrappy, go-to vendor for partners and customers seeing a lot of potential in Asterisk developed deployments.

Channel Chief: Martin Monson

As the videoconferencing and collaboration markets expand, the opportunity for managed services grows, and Glowpoint is among the marquee vendors offering it as a go-to play for partners.

Channel Chief: Khris Kendrick

A VoIP and video surveillance specialist targeting SMBs, Grandstream upped its stake with a new program for agents and resellers. Bigger opportunities meant sharpening its channel chops.

Channel Chief: Stephen DiFranco

Don’t take the world’s largest technology company lightly, especially with HP Networking coming on strong. On tap is HP’s new Visual Collaboration videoconferencing line.

Channel Chief: Rich Hume

IBM is all about alliances, and some of its most pronounced networking partnerships are with top UC vendors like Avaya and scrappier upstarts like ShoreTel. IBM’s UC2 portfolio is well honed.

Channel Chief: William Gildea

It may not grab headlines, but it’s no rookie when it comes to contact center automation, business process automation and enterprise IP telephony.

Channel Chief: Dan Sibille

LifeSize was acquired by Logitech in 2009, but that hasn’t slowed its ascent as the most compelling videoconferencing challenger, positioning itself as a lower-cost, channel-friendly alternative.

Channel Chief: Jon Roskill

It’s called Lync, and it’s Microsoft’s incumbent-scaring UC play: an updated version of its former Office Communications Server that was officially released in December 2010 in 38 languages.

Channel Chief: Philip Keenan

Mitel is a big believer in software’s emerging power in the space and in late 2010 it delivered Freedom, a new UC architecture that delivers UC applications via a cloud-based software stream.

Channel Chief: Larry Levenberg

The brand is perhaps better known in the channel for its top-drawer displays and projectors, but its UC and collaboration portfolios are nothing to sniff at and target SMBs and enterprises.

Channel Chief: Jim Gibb

Strict UC and VoiP vendors are of prime importance, but so are those companies whose products—such as Nuance’s speech and voice recognition

Channel Chief: Donald Houston

Plantronics' UC-centric headset product lines are extensive and thorough affairs. With a well-turned-out channel program and a host of voice alliances, its channel relevancy has never been questioned.

Channel Chief: Ron Myers

A funny thing happened to Polycom as rival Tandberg went to Cisco: It didn’t roll over, it regained channel religion with a retooled partner program and it has broadened its strategic alliances.

Channel Chief: Vic DeBernardis

HD videoconferencing and converged IP telephony are specialties. So is partnering and integration, as in how Radvision’s Scopia UC gateway and other products integrate with top UC-centric platforms.

Channel Chief: Annette Lorenz

ShoreTel may be small compared to UC heavyweight competitors but it’s continued to punch above its weight class and in the past year revamped its channel program, named a new CEO, and bought Agito Networks.

Channel Chief: Patrick Kehoe

It has had more than a few distractions as its financial picture has stabilized, but its UC products and UC and VoIP market acuity have never been in doubut.

Channel Chief: Larry Meyer

Toshiba? In UC and VoiP? Absolutely, for those that have been paying attention. For a crash course, check out the Strata CIX IP business communications systems, aimed at the midmarket.

Channel Chief: Samuel Williams

From UC solutions that combine tools like presence, conferencing and speech recognition to business process automation, Zeacom is no UC rookie. Zeacom Communications Center 5.1 arrived in August.

For more on UC and VoIP providers, check out the 2011 Need To Know: UC & VoIP Emerging Vendors.