If you want to see why a Fixed Mobile Convergence play is a good thing, just look at T-Mobile here in the USA. Their numbers continue to look good, they keep growing and they continually emphasize how well the fledgling T-Mobile @ Home service is doing.
As a user of it, I'm thrilled with its performance to date. It works perfectly, even with all the different routers and networks running in my house. When I travel, I'm able to connect most of the time over my travel router, as long as the hotel's networks aren't all double NAT'd or run in some silly way.
What's more is there's no change in how I make calls...anywhere. Since it always is using my USA number I just dial from the contact directory, giving me the feeling that I'm home, no matter how far away I may be.