The biggest problem you will encounter, assuming you can clobber the NAT and firewall issues, is the wide variation in audio systems across your audience. It won't be easy at all to train your callers to tune their audio systems to your web client prior to calling you.
The FWD ActiveX applet suffers from this problem on top of its limitation to Internet Explorer clients with weakened protection against rogue ActiveX programs.
There are commercial applications available, like GlassHelp (at
http://www.chatessentials.com/main/G...bilities.shtml), but something tells me this would break the budget.