I'm no expert in this stuff, but my next thought would be using Memcache. Of course, do any reading you can on the various ajax chat services out there. The folks at lingr.com posted a nice article on how Lingr works: http://blog.lingr.com/2006/08/lingr_under_the.html (keywords: jetty, comet).
Campfire still uses http polling, but don't knock it! I can go through wifi resets or trips to the coffee shop, and as soon as my wifi connects, it continues right where it left off. Not sure this is very important for a call center though...