OTT messaging is text-based communication on platforms that use existing internet services to deliver messages, including instant messaging applications like Facebook Messenger, WhatsApp, Telegram, LINE, and WeChat. OTT messaging differs from SMS in terms of delivery, fees, user experience, and regulation, with the former relying on the internet and being free to send and receive as long as the device is connected, while the latter requires a mobile network and may charge fees. Businesses can use OTT messaging for customer communications such as notifications, sales interactions, and marketing messages, offering pros like ubiquity, free access, instant personalization, and meeting customers where they prefer to communicate, but also cons like varying application functionality by country and inaccessibility to users without smartphones.