Hello Nina,
if I understood you correctly you would like to know if Exchange Hosted Archive can be used to archive messages of Office Communications.
Microsoft Exchange Hosted Archive (EHA) provides a centralized, easily accessible, and multi-functioning e-mail and IM repository to assist organizations manage increasingly complex retention, compliance, e-discovery, and regulatory requirements.
A variety of Instant Message solutions and Bloomberg messaging are compatible with Exchange Hosted Archive so that IM conversations can also be archived.
For further information please go to: http://download.microsoft.com/download/7/0/3/70330d5c-ffb9-4713-9246-ee26a21051c9/EHS_Hosted_Archive_datasheet.docx or visit http://www.microsoft.com/online/exchange-hosted-services/archive.mspx.
Thanks,
Sarah