I'm glad you state this:
"If these were mobile phone numbers, they could have allowed potential attackers access to customers’ Verizon accounts. This could have then further given the attackers access to online services that were protected by SMS-based two-factor authentication. Once the attackers could be identified as “customers” of Verizon, they could transfer the phone numbers to different phones and then receive the SMS tokens."
Because there was another story recently where someone was able to do exactly this, even without the PIN included in this leak. Human error was at fault there (apparently some operator felt sorry for the scammer) but if you have than PIN, that's the only thing that tells Verizon you are who you are. In that case, the lesson was do not tie a bank account to your PayPal account.
In this case, it appears to be Don't Trust Verizon, they will lie about the severity of the leak.