Equipments and methods for a mediator server controlling communication between clients and service provider(s). Clients are associated with a client identifier address. The mediator uses multiple addresses for receiving communications from the clients regarding the provider(s). The mediator sends to the clients a set of inquiry messages pertaining to the service provider, in a first communication format and associated with a particular reply address. The mediator receives reply message(s) from the clients at the particular reply address, the reply message including the client identifier address and a reply generated at the client terminal device. The mediator sends the client terminal device(s) service continuation information by which the client(s) can continue service provisioning in a second communication format which is different from the first communication format.