The use of the telephone as an interactive medium for promotion and sales WordNet 3.0 & Open English WordNet

Telemarketing is a method of direct marketing in which a salesperson solicits prospective customers to buy products, subscriptions or services, either over the phone or through a subsequent face to face or web conferencing appointment scheduled during the call. Wikipedia

Marketing of goods or services by means of telephone calls, typically unsolicited, to potential customers Wikidata

The business of selling products or services by making unsolicited telephone calls to potential customers. Wiktionary

Selling products or services by making calls to potential customers. Wiktionary (translation)