Web-based IM Client

As a consultant, I often find myself isolated from the team of other consultants in my company. One extremely useful tool that we use is Instant Messaging. It's got all of the goodness of ringing someone's cell phone without the costs associated (using up minutes), and with less disruption. Plus, you can relay URL's and other information via the chat conversation, which are instantly accessible by the recipient (try conveying a complex URL to someone over a cell phone, and you see where I'm coming from).

However, when I work at client sites, I'm often blocked from using any of the IM products that we use (Yahoo and also MSN Messenger) due to overprotective firewall policies. This makes it a real pain for me to ask quick questions, meaning that I have to resort to email or calling a cell phone. And a lot of the time, a person won't check email for hours, or I get voicemail when I call them.

I discovered something a while back, and was reminded of it today by another blog. MSN Messenger has a web-based IM client that will allow me to penetrate the firewall, yet still be able to IM the people using the Win32 client.

http://webmessenger.msn.com/default.aspx?R=1

I think they did a great job with the UI: it looks like a Win32 application, not a web app.

Any other web-based IM success stories?