When was the last time you pulled over your car and wrote down a phone number?
Aside from some vanity numbers with a word in them, phone numbers are not memorable. Plus today, most people will do online research before they decide to call a business. Effective radio ads are about branding and getting the advertiser known, getting prospects into the client’s business funnel, and to their website where more of the sale is made.
So no, putting the phone number in the commercial is not a good idea. I think the best use of the 7 seconds it takes to add a phone number people won’t remember is to reinforce the web URL. Put the phone number (and all ways to contact the advertiser) on the advertiser’s website, then with every message, direct people to that website.
Is there an exception? Of course, if the goal of the ad is to get your number saved into a listener’s phone. A tow company for example, or a taxi company, will benefit from having their number in a listener’s phone, just in case of emergency. That’s just another way of building top-of-mind-awareness. In this case, though, the ad is entirely about getting the number saved and not referring to a web page, or anywhere else.