The present invention generally relates to data transmission services in mobile communication systems. A mobile subscriber may typically be entitled to different kinds of tele and bearer services. Presently, each user data rate is an independent bearer service. This means that there is a vast number of bearer services, which causes problems for both the network operators and the mobile subscribers. According to the invention, the number of bearer services is reduced by defining the bearer service to cover several data rates, and by negotiating, at the call set-up stage, the data rate to be used by the data call in the bearer service between the mobile station (MS) and the mobile communication network (MSC). The next step is to negotiate the data rate between the mobile communication network (MSC) and the fixed network, such as PSTN or ISDN. Then, if required, the data rate of the mobile communication network and the radio channel resources are adapted to the data rate used towards the fixed network.