i suggest to add reply to the ad option on the same ad page. this is like what we use to do on facebook. its very time taking process to take the number from ad and send whatsapp, sms or call. Your page will be revolutionize if you add this option to the ads. the reader will be able to directly ask any queries on the page as well as the ad initiator will also be able to reply only once for multiple similar queries. also others can see the response of a query.