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.