No - it is not a secure personal identifier (in many countries). According to Australian laws, someone can port your mobile number to his/her sim card by filin

No - it is not a secure personal identifier (in many countries). According to Australian laws, someone can port your mobile number to his/her sim card by filing an online form, as long as they know your date of birth and account number, that person can take your phone number away in minutes. Nothing need to be done in person, no ID will be asked. In fact, the laws are made to explicitly forbid such checks under the name of giving consumers easy way to transfer to a different provider. You will get a SMS on your phone notifying you that someone has ported your number away and the next thing that is going to happen is that the offender is going to recover your paypal/gmail/online banking password using your phone number - time to say goodbye to your money in your account. The story here is simple - phone numbers are misued by many as some kind of personal identifier, it is a feature with close to zero security protection in many countries. Mobile providers don't have any motivation to further secure it as they never claimed it to be secure and they didn't make $ out of it.