When you first setup GV, you will need to be at the phone to set it up. So, your theory would work if you were setting up the GV for them. Let’s say you setup a GV account for your friend using a dummy gmail account. Then they want to get a GV account and then can’t because you have used their phone number already.

It could work, but only if you know your friend is not going to get a GV account, and they are their to help you sign up, since they call the phone number and ask for a security code..

Does that make sense?