is not easy to get the info directly from the bus running to the the LCD, first you have to know what kind of transmission is using the LCD it may be 4, or 8 bits (plus 2 or 3 pins for signalling) or serial trans.
sometimes the chip controls the LCD, so it will be hard to get the info. usually LCD´s are driven by their own microcontroller and other chip send the info to it.
what youre trying to do is used frequently to put info into Publiks (electronic visual devices or signboards). sometimes beepers are allowed to have one pin to transmit serial data to other devices, may you contact the manufacturer and ask directly or search for a beeper with those characteristics, ask to any publik developer or ask to a beeper company to get the service.
killa