God... Imagine being in the middle of an important call for say discussing family affairs for a dying family member and you just hear "there will be a 30 second advertisement break in 1 minute."... I'd probably pop a blood vessel.
Your dialer may already be monetized! If you get a call from a company and see their logo chances are they paid for that. It's not enshittified yet, but it definitely could be. Source: I maintain a codebase that does this for a major device manufacturers dialer.