Ive seen some enterprise level voip providers in the UK not only provide clients with VOIP systems either on site or a cloud PBX, but also a dedicated leased ADSL line. Usually 2mbps both up / down (They say this is good for about 20 concurrent users). They also connect the the line directly to their voip server, so it dosnt have to make multiple hops.

Never tried one in practice though. We run our voip over our main 200mbps down, 15 up fibre connection. Have QOS and VOIP prioritisation setup on the router, SIP ALG off etc. Seems pretty good, but as you said, if you know what to look for you can always tell your on a voip call.