There is a new (July 2010) update for Office Communicator Mobile 2007 R2. Knowledge base article 969816 describes the issues that it fixes and how to install it. Note: this KB article looks to be old (July 2009).
You can download the update here: http://www.microsoft.com/downloads/details.aspx?displaylang=en&FamilyID=93062936-f216-4d97-aa13-105a20454322.
Note: Microsoft recommends that you uninstall all prior versions of Communicator Mobile before installing the new version. This will bring update your CoMo version to 6906.29.