You can get Microsoft Office Communicator Mobile 2007 R2 (CommunicatorMobile.PPC.msi) or (CommunicatorMobile.SP.msi here). As per the article “Installing Communicator Mobile for Windows Mobile from a Storage Card Link” you need to have a .CAB file, by default only .MSI is downloadable from the Microsoft Website. You can install the Communicator Client via ActiveSync Installing Communicator Mobile Using ActiveSync 4.5 Ref Link. You can use CommunicatorMobile.MSI file to install CommunicatorMobile on the Windows Mobile.
Full Article: OCS Team