Normally, if you want to install Office Communicator Mobile on your phone you have to do so by running an MSI on you PC, then sync your phone to install the application through ActiveSync. If you prefer to just install directly from the .cab file, you can browse to www.getcomo.com (this is a Microsoft website) on your mobile phone, choose your phones OS, then install the .cab directly from the website, no PC or syncing involved!