It's no surprise that Cisco Systems came out on top as the leading vendor for solution providers when it comes to VoIP. But there is a host of challengers nipping at Cisco's heels, according to findings in the 2009 CRN Channel Contenders survey. The research sought to identify the top vendors that solution providers choose as alternatives to market leaders. Here are the top 10 contenders for VoIP.

Cisco Systems isn't happy with just the No. 1 spot -- it also needs to be No. 2. Cisco's Linksys arm, which used to focus on SMB and consumer markets and now is just a consumer brand, was selected as the strongest challenger to, well, Cisco when it comes to VoIP. Linksys offers affordable solutions for smaller deployments, where its parent targets larger enterprises with more sophisticated needs.

Solution providers polled consider Nortel Networks a Channel Contender for its incumbent VoIP offering. It's no surprise. Nortel built its name on legacy TDM and grew into VoIP and unified communications at just the right time. While Nortel's future in VoIP may be uncertain as it navigates Chapter 11 bankruptcy protection, it still has the chops in the VoIP arena to keep plugging along as Nortel TDM customers look to upgrade to the VoIP world. As of this writing, Nortel was looking to auction off its enterprise solutions business, which includes its VoIP solutions, and Avaya is the lead bidder with an offer of $475 million.

Channel Contender respondents also consider ShoreTel a strong alternative to Cisco. ShoreTel is a pure play VoIP and UC provider bent on helping companies of any size integrate communications, data, messaging and business processes regardless of device or location. ShoreTel's technology stands out as a distributed software architecture that cuts out the traditional costs, complexity and reliability issues associated with a host of other VoIP and UC vendors.

Avaya takes on straight-up VoIP, UC and call center deployments with hardware and software features that keep it top of mind and a true force to reckon with. This year, Avaya unveiled Aura, an all-in-one SIP-based UC platform that integrates across multivendor environments, multiple locations and several business modes to deliver voice, video, messaging, presence, Web applications and more while also reducing communication network complexity and infrastructure costs. Avaya is currently the lead dog in the running to acquire Nortel's Enterprise Solutions business with a bid of $475 million, which would only make it a stronger contender to Cisco's throne.

Alcatel-Lucent may not be the communications powerhouse its two components were before joining forces, but solution providers polled said the French company is still a solid Channel Contender. Alcatel-Lucent can ease the TDM to IP telephony transition and offer hybrids of the two while hitting the midmarket and large enterprise in one fell swoop.

3Com may have transformed its enterprise networking offerings earlier this year, but its VoIP solutions, which have been key to the company's continued success, aren't going anywhere. Its convergence strategy of "one IP network, many applications" sets it apart from the pack and makes it a strong player in the crowded VoIP space.

Polycom has clawed its way into nearly every VoIP conversation with its innovative line of video, voice, telepresence and wireless hardware and software offerings. Polycom continues to break the mold in desktop telephones, building high-quality devices that tie in a host of robust features, including access to communications applications and information at the touch of a finger. The recent addition of Microsoft's former RoundTable offering, now the Polycom CX5000, will keep that strategy going.

No one VoIP vendor has sparked more debate than Microsoft, storming the market a couple of years back with its Office Communication Server (OCS) offering and essentially calling for the death of the PBX. Well, Microsoft's software-driven approach to VoIP is gathering steam and some companies are going PBX-free. In the VoIP world, you're either for Microsoft or against it, and enough VARs queried for Channel Contenders said they're for it and see it as a strong alternative vendor.

Open-source VoIP has started to take hold, and it's no wonder the pioneer of the open-source VoIP revolution, Asterisk, is being seen as a viable alternative. Digium delivers the hardware and software based on Asterisk code to make an open-source VoIP deployment a reality. Aimed mostly at SMBs, Digium and Asterisk have become the most widely used open-source telephony platform.

D-Link is digging deep into VoIP, putting its switches and routers to work with a host of recent VoIP solutions for the SMB and the large enterprise alike. D-Link recently revealed its new line of VoIP gear, which includes phone systems, gateways and desktop phones that integrate Microsoft's Response Point. D-Link also leverages IP in other ways, making itself a leader in IP video surveillance gear. D-Link is seen as an alternative because of its wide reach (available in more than 130 countries), its affordability and the company's ability to churn out gear that works and works well.