Mobility in cellular networks requires to manage handovers, which occur as users move from one cell to another. Their effects, which are easily overcome for speech, may seriously affect data transmissions. In this paper we report about tests for evaluating the quality of transmission for data applications on a GSM cellular network. Static tests, consisting of file transfers on PSTN and on GSM networks with the MS located in a fixed place, have evidenced a substantial stability and reliability of the GSM radio link, while the throughput over the GSM link is smaller than that measured over PSTN of an amount depending on the packet size. Dynamic tests, consisting of file transfers on GSM with the MS moving along a selected path where transition borders between adjacent cells could be encountered, proved that the transition through the border region between adjacent cells appears to be quite critical and often causes the interruption of the transmission.