Committers and contributors can often be found hanging out in IRC. Below is the information about the channel that we use: 

Server: irc.freenode.net

Channel: #apache-activemq

There are many IRC clients available out there depending on the operating system you are using. 

Note the IRC channel on codehaus is deprecated as of April 2015; please refrain from using that room.  Likewise, be aware there is a channel named #activemq on the freenode server - please avoid it as well.