Your edit is correct. And the Google Voice instructions posted at the above link right now are clear: you do not need to interact with your old carrier to get

Your edit is correct. And the Google Voice instructions posted at the above link right now are clear: you do not need to interact with your old carrier to get your number on Google Voice. I have tried it myself. I believe what I outlined turns "Something you know and something you have" into "Something you know and something you once had for a minute at a different point in time." This is a significant to the 2FA security model, because the victim may mistakenly believe that even when left alone with her phone, especially if the phone requires a code to access (which is often not needed to answer a call), you would not be able to take control of her accounts unless you were simultaneously using a computer to do so. All you need is to click the "Verify" button on your Google account at the right time, which would likely go unnoticed.