I was recently asked about Yammer and SharePoint integration by a customer and I got some information which I had sent them. Just for a reference here is that info:
Microsoft will be making announcements about the Cloud service it will provide for Yammer on 11/12/2012
There is the possibility to have some integration between Yammer and on-premises SharePoint Farms, like Web Parts and Federated Search or sync of profiles from SharePoint to yammer please read the following for more information https://www.yammer.com/company/sharepoint/
Then this morning as I was driving in it hit me that if you want on-prem Microblogging, look no further then SharePoint 2013 Newsfeeds, I believe that the SharePoint Product Group is positioning that as the MicroBlogging platform within the enterprise. Some of the features that you will see:
Support for common microblog terms like @Mention or #Tags
Able to follow people or #Tags
Using various technologies it would be possible to create a phone app (Windows, IOS, or Droid) This would of course require that mysites are published to the internet.
We are already using this technology at Microsoft and I think it looks great.
Overview of microblog features, feeds, and the Distributed Cache service in SharePoint Server 2013