There are ready to go solutions for that identifying specific applications (VoIP would be one of them) down to the provider of the solution (e.g Facebook, Skype

There are ready to go solutions for that identifying specific applications (VoIP would be one of them) down to the provider of the solution (e.g Facebook, Skype). And yes this is done via DPI plus patterns etc. So it would not really matter (on the long run) if you would e.g. tunnel that on port 80. Most providers of such solutions by now fully integrate with the Telco's management platforms similar to "plug-ins". Current market estimates for these platforms (policy servers) and DPI are expected to grow to more than $5B over the next years. In Telco environments these things are generally covered under traffic management and the acronyms PCC or PCRF. I think TeliaSonera is using OpeNet in some of their countries since quite some time for that at least with 4G.