red to utilise a particular service using any or all of the following terminals or appliances: [0075] a GSM mobile client 13 a connected via a GSM cell site 23 and SMSC server system 25, where SMS messages 27 are transmitted between a GSM device 29 of the client, such as a mobile phone, and the SMSC server system 25, [0076] a PC-based client 13 b connected via an Internet Service Provider (???ISP?