Abstract: A telecommunications network (1) comprises a plurality of base transceiver stations (BTSs) (3). According to one embodiment, data is transferred to a BTS (3) via a test mobile station (5) and serving cell (15). The best mobile station (5) is connected to the BTS (3) via a high-speed data connection (11), for example an ATM link, thereby enabling data to be transferred to the BTS (3) at high speed. The data may also be transferred to the test mobile station (5) using the overlapping radio interface coverage (19) of another, in service, BTS (17). This aspect of the invention allows data to be transferred to a BTS (3) before it is commissioned or entered into service.