In February\u00a0we challenged \u00a0some of the largest IP PBX suppliers to come to the Voice on the Net show at the end of this month in San Jose to discuss just what it is that makes their products stand apart.After all, we are at that stage in the development of this market. The shroud of mystery surrounding the technology is gone, we know how the products work, early adopters are having success, and now the pressure is on vendors to differentiate wares that, on the face of it, look increasingly similar.All the vendors we called on have taken up the gauntlet. The participants are:\u2022 Alcatel: Jeanne Bayerl, director of product marketing, Alcatel eBusiness Networking division.\u2022 Avaya: Mack Leathurby, director, converged system and unified communication applications\/portfolio products and solutions marketing.\u2022 Cisco: Marthin DeBeer, vice president and general manager, enterprise voice and video business unit.\u2022 Mitel: Christian Szpilfogel, director of product line management for enterprise platforms.\u2022 Nortel: Tony Pereira, director, enterprise solutions marketing.Yours truly and co-host Mike Hommer, manager of consulting for Miercom, which is a member of the Network World Global Test Alliance, will try to pin down these folks on the core differences between their respective products.While that debate undoubtedly will touch on technology, we will focus on features, functions and capabilities - everything from management tools to security options, call center support to unified messaging, station alternatives to ROI.The goal, of course, is for attendees in the room to walk away with a better idea of where the core IP PBX vendors stand on a range of topics, any subset of which would be important to different types of deployments.After Hommer and I pester each vendor, the manufacturers will be given the chance to grill each other in this classic debate format, and then we'll wrap it up by throwing it open to questions from the audience.These things usually are lively and revealing, so if you're considering voice over IP, try to make it to this Network World Showdown, "IP PBXs: Telling the players apart," from 5 to 6:30 p.m. March 31 at Spring VON at the San Jose Convention Center. (To register for VON, go to\u00a0VON.com.)In the meantime, send along any questions you would like to see the IP PBX vendors address.