The deal is the third the companies have signed over the years, but like the others, terms of this deal were not disclosed.
The announcement came at the annual IT Expo and Conference going on this week in Las Vegas.
On Tuesday, Microsoft and HP announced a four-year to invest as much as $180 million in building a complete corporate infrastructure for unified communications and collaboration. The deal was short on specifics, but revolved around Microsoft's SharePoint Server, Exchange Server and Office Communications Server (OCS), and HP's ProCurve networking hardware and Halo Telepresence audio/visual technology.
In addition, HP plans to certify for OCS its HP dx9000 TouchSmart Business PC and specific models of its smartphones. HP also will develop IP desk phones certified for the Microsoft UC infrastructure
The pair also said they could collaborate on new product development. That and the entire product integration project would be made easier if the two had an agreement in place to share intellectual property.