The call to action goes at the very very end of the ad.
Why? Because the Call to Action signals that an ad has finished. We've tested it: listeners miss anything that occurs after the Call to Action. So if you want your "kicker", "hotchka" or "punchline" to be heard, put it before the Call to Action
In "offer" ads the offer goes first.
In every self-respecting print ad the headline screams the offer. On radio, the headline is your opening line so same-same for radio offer ads (apart from the scream. Tho’ now I mention it hmmmmm.)
Phone numbers and URLs work in radio ads
If anyone tells you different - they're regurgitating an old unfounded radio "fact". Those listeners who are still paying attention to your ad by the Call-to-Action want the phone number or the URL. By the way if you ever start an ad with a phone number you deserve to have your organs harvested prematurely.
Speed kills - quickly and slowly
Fast ads are annoying - slow ads are boring. Both make listeners tune out. At an easy to follow pace 80 words is 30 seconds.