Essentially, there are four (soon to be five) nationwide fiber networks.
Actually, Kent, there are six. IXC Communications is building out its
fiber network as well.
What you've said about route diversity is right. With nearly all the
carriers involved in leasing from each other, fiber swaps, and joint
fiber builds, diversity is not assured just by going with different
providers. Grooming complicates the picture too, but I have to agree
that if you've contracted with a provider for diversity on their routes,
you should get it even if the route is groomed.