A telecommunication system intended for providing telecommunication services at a semiconductor manufacturing plant under the circumstances of shielded areas of clean rooms comprises a GSM base station installed at the plant and equipped with a plurality of low power antennas, a private branch exchange and at least two dedicated lines of E1 type connecting the base station and the PBX to a public switched telephone network. Software incorporated in the base station and PBX allows for telecommunication connections set up at the plant to use abbreviated four-digit numbers for both wireless mobile stations and wired stations, while keeping the possibility to reach a mobile station, even if it is outside the plant at the time of the connection, dialing the abbreviated four-digit number.