It is quite usual for enterprises to have multiple IP bandwidth links. That increases churn in business IP trunking. Obviously as a service provider, you would try to provide better QoS in order to counter that churn. If however your partner carriers use voice quality solutions from different vendors, I am told that you would have problems implementing QoS end-to-end. Twelve years of VoIP and you still have interop issues!
There are over 65 million fixed line VoIP subscribers worldwide. Nearly all of them – as well as a lot of business VoIP customers - are being served by public Internet. Being able to manage voice quality over public Internet has to be an important issue unless the service providers are content with keeping VoIP as a secondary option. Most of the service providers are burying their heads in the sand hoping the bandwidth in the backbones will remain abundant. That is a bad assumption. Shared transportation will not always work, especially since video is going to consume a lot of capacity.
Apparently there is an IETF standard in place that helps a service provider establish and report QoS. Several core and CPE vendors have implemented it. But that is QoS between the service provider and its customers. Once the call leaves a service provider’s network, there is no quality assurance!
There is very little work going on within the industry to standardize how these quality assurance measures can be taken and implemented. Some joint work is going on between QoS solution vendors and service providers. However they are bilateral and not multi-lateral initiatives. There was of course something called RSVP that promised cross-network QoS a long time ago. That technology has perhaps remained confined to academic research.