Facebook, Twitter, Skype, Gmail, etc. whether they charge users a fee or not, all present themselves as basic infrastructure services, with an implied expectation that if you register a name with them, that's as good as having a phone number, and it will not be taken away from you unless the service is discontinued.
Legally speaking, Twitter is probably okay here, but if Facebook or Google did the same thing, I would expect they could be legally liable. Google's TOS for example states:
>We take appropriate security measures to protect against unauthorized access to or unauthorized alteration, disclosure or destruction of data. These include internal reviews of our data collection, storage and processing practices and security measures, including appropriate encryption and physical security measures to guard against unauthorized access to systems where we store personal data.
It's reasonable to assume that people are using Gmail as a verification email for other services, so they could actually be breaching their own TOS by giving someone's username to someone else, since when you've used a Gmail account for even three months, it becomes personal information that should be protected.
Ethically speaking, all services should be doing due diligence when reassigning usernames. This isn't IRC, all of these services are marketing themselves as identity gateways, and reassigning identities without cause borders on outright fraud. In this case of course, they're actually acting as they normally do, trying to make sure that online identities match legal identities, so it's more understandable, and probably protects them from allegations that they're facilitating fraud. But your authoritarian system is ethically dubious, and furthermore unlikely to hold up in a court of law.
> you seems to take a mental image created in your head by marketing for a contract fine print.
Representations given to a user ("marketing") can constitute an implied contract, or at least a cause of action if they aren't fulfilled. It'd be one thing if Google said up front that their service should be considered unreliable, and may be discontinued at any time, or user accounts even arbitrarily given to third parties. But if they claim otherwise up front, that can be at least somewhat legally binding. Not sure how a court case would turn out, but they aren't automatically in the clear.
Now you are paying for the service and if you stop paying for service it can go to anyone, but that's not the carrier's decision. Telephone numbers are federally regulated.
The Wikipedia article on telephone numbers also suggests that the bureaucracy managing them tries to avoid reassigning disconnected numbers if those numbers are still receiving regular calls. And this makes sense, since people receiving messages intended for someone else is bad for operators, and bad for the users.
As others have noted, there may even be regulations [1] that apply here, though Twitter seems pretty safe from a legal perspective, even if ethically they're in the wrong.
Legally speaking, Twitter is probably okay here, but if Facebook or Google did the same thing, I would expect they could be legally liable. Google's TOS for example states:
>We take appropriate security measures to protect against unauthorized access to or unauthorized alteration, disclosure or destruction of data. These include internal reviews of our data collection, storage and processing practices and security measures, including appropriate encryption and physical security measures to guard against unauthorized access to systems where we store personal data.
It's reasonable to assume that people are using Gmail as a verification email for other services, so they could actually be breaching their own TOS by giving someone's username to someone else, since when you've used a Gmail account for even three months, it becomes personal information that should be protected.
Ethically speaking, all services should be doing due diligence when reassigning usernames. This isn't IRC, all of these services are marketing themselves as identity gateways, and reassigning identities without cause borders on outright fraud. In this case of course, they're actually acting as they normally do, trying to make sure that online identities match legal identities, so it's more understandable, and probably protects them from allegations that they're facilitating fraud. But your authoritarian system is ethically dubious, and furthermore unlikely to hold up in a court of law.