[1]: http://krebsonsecurity.com/2015/12/2016-reality-lazy-authent...
[2]: https://medium.com/@espringe/amazon-s-customer-service-backd...
https://youtu.be/bjYhmX_OUQQ?t=2m30s
A phone provider's key goal is to continue to provide charged-for services to their customers, not to secure your bank account or dns registrar account... They'll do whatever's needed to allow paying customers to pay or pay more.
Alhough as a customer, I'd like my phones not to be redirect to anybody asking for it, but I understand they don't have the security measures a bank should have.
It's a password that you reuse everywhere and never change.
"The SSA may assign a new Social Security numberto you if you are being harassed, abused, or are in grave danger when using the original number, or if you can prove that someone has stolen your number and is using it."
Unfortunately, maintaining and securing a private email server can be a big job. Google already does that job, and their data centers are much more secure than the VPS provider where you'll host your private email server.
All I'm asking for -- and I don't think this is unreasonable -- is to rely on their world-class technical security, while being able to disable all password recovery methods, which are vulnerable to social engineering.
All the target knows is, his phone has been forwarded and his Gmail password changed. Even assuming the police are willing to help (which is unlikely), all they'll discover is that your phone number is forwarding to a disposable cell phone which was bought with cash.
It worries me, though, that they're willing to accommodate novices to such a degree that they open up advanced users to targeted attacks. For example, Gmail bugs you quite a bit to set a "recovery phone number," but doesn't make it clear that this isn't like 2-factor auth. The phone number is actually a single factor that can be used to reset your password. It even works if you have "traditional" 2-factor enabled.
Thus, the attack looks like this:
1. Look up target's social security number. This is easy with certain online services that were meant for private investigators, but actually let anyone get an account.
2. Contact their cell phone provider. If you don't know which one, guess. There are only a handful of common providers and you'll hit on it eventually. Impersonate the target, say you're going on vacation and need your calls and texts forwarded, and give them the SSN from step 1 to verify.
3. Go to Gmail and say you forgot your password. Opt for the phone based reset, and wait for the text with a reset token to come in. Ideally, do this while the target is asleep to give yourself time to work.
High profile individuals have actually been hit this way, and I think Gmail should offer greater protection to sophisticated users who do everything right, don't fall for phishing, and would never forget their password, but can fall victim to highly targeted attacks.
[1] https://www.youtube.com/watch?v=nkV9kOsTyJU