The Play Store notified me of the UCA upgrade. Installed without issue. Still can't IM to other users and still assume that upgrade to UCA Server 5 is required for IM from Mobile Phone to desktop - which I can understand.
Is there a good link on the whole "OfficeLink" aspect of the mobile client? I have no understanding of it and how it's supposed to work. I'm sure it's a RTFM issue, but would be great to be pointed in the right direction.