This is not really an issue with the TP2. I dealt with the exact same issue when my company deployed OWA and Webchat (CWA). iPhones worked like a champ and WinMo phones didn't.
The reason is that the iPhone's access CWA (communicator web access) via their Safari web browser. You're trying to access webchat using Communicator Mobile. This will never work. Instead, access the site using Pocket IE or Opera. CWA can only be accessed from a web browser. I was successfully able to get to your company's webchat login page from my TP2.
The CoMo client accesses the OCS server exactly like the full Communicator client. Therefore, if you want to use the CoMo client on your TP2 then you need to ask your Exchange/OCS administrator to deploy the OCS server to the Internet (using ISA 2006)
Hope this helps.