There aren't alternatives to a telephone system: there is essentially 'one' telephone. What's App is hardly a monopoly. Users could use SMS, Skype or any number of alternatives that provide almost identical utility. It isn't like comparing a telephone with hand written notes.

Interestingly, what led to What's App? Telephone company monopolies on SMS. The internet itself could be considered a public utility -- not what flows over its wires.

One solution to this, assuming we want to take the public utility route, is to start charging users like it were a utility. Perhaps €10 per month for German users to offset the lost revenue from the data FB won't be allowed to collect. Then the Germans can tax that €10 just like it taxes phones and everyone will be happy. What's App isn't 'free.' Using that service has a cost. Should Facebook just give away their product? Why would a business do that? Facebook employees don't work for free, so why should Germans get to free ride? A really popular service ought not be regulated by the virtue that it's really popular.

There is a mostly free market. What's App isn't essential or even necessary. It's about as 'vital' as Instagram. It isn't like it's the only game in town.. not even close.