The problem I see is that people use their personal devices for work or work devices for personal. It should be the individual's responsibility to separate their work life from their personal life.
A company can't force you to use your personal property for work--so don't do it. If you are trying to be a cheapskate and use your work phone or notebook for your personal business, you are a) setting yourself up to be inundated with company communication during work hours and b) allowing your company to snoop on you because after all it is their phone. Go and buy a separate phone or notebook for your personal life that doesn't have your work communication associated with it. Then leave your work devices off. Problem solved.
I think it is ludicrous that a company has to shut it's email servers down at night and weekends. There are different parts of a large organization that doesn't fit into the 9 to 5 mold. If I were the CIO at Volkswagen I would create an employee policy that requires employees to separate their work and personal digital lives. And it is the employee's responsibility to keep their personal and work life separate. Additionally, emails with company domains not be used for ANY personal communication of any kind. This protects the employee's privacy, it protects the company's reputation in regards to public blog posts and illicit websites, and it lowers the amount of spam/marketing emails the company email servers need to deal with.
I worked for a large company with over 2000 employees and a clueless CIO. I managed the web development team and tried to convince them to have a stiffer work vs personal policy (also to use Linux and open source software, but that's another story). But corporate structures being the way they are, I could never get much traction.