Update: Re-routing my phone's mobile data connection trough VPN to my home network has solved the problem.

Phone on Wifi @ home : Nuvi got data.
Phone on mobile data: Nuvi can't connect to any service
Phone on mobile data, with VPN to home-network: Nuvi got data.

It's a strange thought in these days of free internet use without restrictions: could it be that my mobile provider ( KPN, Netherlands) is blocking certain datastreams/protocols, in effect making the smartphone-link connections impossible?

But for now i'm happy, got my trafficinfo working 100% :D