There will now be two backbones sharing the same pool of customers, thus the fixed costs will have to be recovered fro, whatever the fraction of customers you can lure away is, not the whole market as it was before.
Given that the story says:
As Bell was given a last-mile monopoly in much of Canada by the government they are required to follow rules set up by the CRTC this includes leasing their lines to competitive ISPs.
"Much of Canada" must be a significant amount of customers and I think you would need to consider that whatever new company would compete against Bell would try to offer some nice incentives to attract customers. They would probably push the status quo and consumers would get the best.
I know your point is that it doesn't seem to make much sense for a company in terms of profit but although the profits might not be the same as that of a natural monopoly, I think the profits of an oligopoly would still be attractive.
Yes, prepaid or "as you go" service is the most popular kind of cellphone service in Mexico. I read some time ago that it was even bigger than land lines. I can't find the link where I read that but this says something similar.
From the article you need to provide name, date of birth and CURP if you are registering via SMS (you might be asked to provide gender and state of residence). However, to get a new cellphone number you would also need to provide a fingerprint, proof of address (like a hydro bill) and a valid id (I'm guessing voting card or passport).
"You can't get very far in this world without your dossier being there first." -- Arthur Miller