I have this on Windows 7 and love it. I want to get it on the iPhone too. Plus, does anyone know if it's available for the Mac? Can't find it.
The Mac version is still in the Alpha stage of testing. You can sign up to test the Beta version whenever it's released. Just go to the developer's download page and click the signup link.
You can use the web version on the Mac for now until the official OS X version moves to beta.
I like Trillian on the iPhone, but I'm looking forward to some updates in the near future