Rebtel is a communication company that offers various services such as international calling, messaging, and mobile top-ups. They provide mobile apps for iOS and Android, web-based calling, and SMS messaging. With Rebtel, customers can make affordable international calls without an internet connection, send SMS messages, and top up mobile phones in over 100 countries. The company is known for its reliability and affordability, making it a preferred choice for those seeking an alternative to traditional telecom providers.