When I was getting a new line for some relatives, I found that when going through the web checkout process you could select your phone number out of 5 choices before completing the purchase. I thought that was pretty bad design as it shows which numbers are most likely going to be new. It would be pretty easy to scrape that page and create a spam list.
Sure enough, it didn't take long for the new number to start receiving spam.
At least that election season won't last more than 7 weeks. Instead of this insane 2 year marathon the US has.