NSN manages to pull off the feat by creating phantom (virtual) channels that "supplement the two physical wires that are the standard configuration for copper transmission lines." First shown off by Alcatel-Lucent's Bell Labs in April 2010, the approach is called Phantom DSL and can boost bandwidth between 50 to 75 percent over existing bonded copper lines. "Laying down new optical fiber to the home remains costly, though it is capable of delivering very high speeds and is a definite solution for long-term bandwidth requirements, Eduard Scheiterer, NSN's head of broadband access business line, said in a statement. "However, the innovative use of technologies such as phantom circuits helps operators provide an efficient last mile connectivity with existing copper wires."
It is quite surprising to see DSL technologies based on copper wiring staying competitive with cable broadband and fiber. Upgrades in DSL speeds are coming at a useful time: DSL has started to lose market momentum, and carriers don't want to just drop it after all the money they've already invested. While fiber networks are better in the long run, most phone companies need to squeeze out more from their copper networks without losing too much ground to cable broadband rivals as the world shifts to wireless networks. That being said, these new DSL technologies are still in the labs and may not work very well over long distances, not to mention all the other technical restrictions. Somehow we doubt you'll ever get 800Mbps at home, from DSL anyway.