Richard Stastny in his VoIP and ENUM has an interesting post on the debate as to whether "SIP is dead" versus Skype versus NGN:
- So the real fight will take place between the planned IMS NGN and the existing Skype NGN, having a headstart of approx. two years. If the IMS NGN will be able to catch up will be decided finally by the customer, because he will be able to choose on his mobile device if he is using the IMS NGN VoIP or the Skype NGN VoIP. Of course one can download a SIP client also on a Smartphone, try to configure it (good luck) and register with a free SIP provider, , in case there are any left. Then he may be reached via his SIP URI and also contact anybody with a SIP URI, if thery are any. Metcalfe's will be against this approach.