A plurality of clients for different users use on-line services via a mobile communications network in a system comprising: an application database for holding a group of different applications for providing associated services to a client, the applications being configured to provide clients with unlimited off-line use and limited on-line use, an account database for keeping record of the amount of available on-line use of different services provided to the client and an on-line service controller for running on-line services with different clients and for causing the account database to reduce in a predetermined manner the amount of available on-line use when the client uses the on-line service, if the on-line use is allowed. The clients are capable of obtaining a desired application from the application database via the mobile communications network, running the desired application off-line unrestrictedly when desired by the user, and running the application in communication with the on-line service controller using the mobile communications network to use the on-line service associated with the desired application when desired by the user of the client. Corresponding methods, apparatus and computer programs have also been disclosed.