The invention relates to a method and system for booking reservations in a booking system and synchronizing bookings among several booking systems. The system comprises at least one booking system; at least one service provider; a mediator service; a client, and at least one client terminal device that can be a mobile device and that includes a dialogue. The client uses the dialogue to enter information into the system and the mediator receives inquiries and answers from the at least one booking system, the at least one service provider, and the at least one client. The mediator transfers and adapts information between them. The method and system are particularly suited for use with mobile phone users by Small Message Service messages.