For those providers who already have their phone traffic routed over IP, it will be straightforward, and software controlled. I am not sure how many are actually in that position, but there must be plenty of others not at that stage yet.
As far as the physical connections, I am referring back about 14 years, when interconnections were made on very large DDFs (Digital Distribution Frames). As the migration to IP is fairly recent, I cannot imagine all of those connections no longer exist. Others on this forum who have worked for BT, will know what I mean.
Personally I would take all of the estimates to fix all of the routing as optimistic, because unless there have been very accurate historic records kept, there are going to be missing routes from certain providers, maybe only affecting certain exchanges.
Anyway, its a bit off-topic now, but I hope its gives some idea of problem that may arise, so lets see how long it really takes, remembering of course that every provider that moves to VOIP, are going to face the same routing problems.
Fortunately the mobile network does not normally suffer from this problem, otherwise moving from one provider to another, would not be as easy as it is now.
