radio telephone apparatus for use in a cellular mobile telephone system comprises means for alarming at least a user operating the apparatus in response to a drop in signal strength of radio frequency signals received over an established communication channel when the apparatus approaches a boundary of service area in a cellular mobile telephone system . the signal strength is repetitively checked to determine if it has fallen below a first predetermined signal strength value . when the signal strength falls to or below a second predetermined signal strength value , the radio telephone apparatus causes a disconnection of the telephone link and returns the apparatus to a standby mode .