I was concerned about this, but when I looked into it today (10/7/2019) it appears that perhaps the procedure has changed. It appears that they now generate a unique PIN on-the-fly.
"If you are transferring your phone number, your new carrier will ask you for a PIN. For your security, Xfinity Mobile generates a unique security PIN upon request.
Below, select the active line where we can send an SMS with your security PIN. The same security PIN can be used to transfer any number on your account. It will expire in five days."
So, if you can keep your XM account secure (and don't lose your phone), does this mean your phone number is safe?
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