Just started a trial of LiveChat (www.livechatinc.com) having met up with Gareth Thompson (@cssgareth for those on Twitter) of CodePotato for a pizza on Friday/end of April 2012. Be careful to get the right LiveChat or else you will be looking at something very different! LiveChat is not cheap but can be used on more than one website. It allows you to put a "chat now" box on as many or as few pages as you want with great customisability. If you are not online then the prospect can simply "leave a message". It comes with a WordPress plugin and apps for Android and Apple. Perhaps most important of all is the robust desktop application for Windows and Mac. This allows you to be logged in (or another operator in your office) to answer LiveChat.
Anyway the thing about a free trial, such that LiveChat offer, you only need a "heads up" from us - if it spikes your interest you can start the trial at www.livechatinc.com
In terms of the "how" we are using it. More on that behind the login.