It is as simple as that. We will need both, and one does not replace the other. Any data rate comparison is futile exercise, since the mobile applications are completely different from those applications you would use sitting in front of a large screen at home at office. However, a critical market reality to understand is that, out side of the United States, due to lower percentage of PC penetration and far higher degree of mobile penetration, mobile devices will become far more predominant Internet appliances, far exceeding any fixed devices using fiber, cable or Ethernet. Thus the opportunity for startup companies to recognize this trend and capitalize on it.
Fixed substitution is limited to situations where such speeds are adequate.
3G is primarily about services in which mobility is the key attribute. In my view, NTT DoCoMo's dominant position in Japan did play a role in its success with I-Mode. However, it was only one of the reasons. There are lots of telecom companies around the world, especially in Europe, that are dominant in their national markets, but have not been so successful with such initiatives. Not sure that regulation is the issue.