Considering all the suggestions I have decided not to use EEPROM as that would cause too many delays, since the controller is also supposed to scroll the LED display apart from reading the serial data and writing it to memory somwhere. I will now simply get a microcontroller with a large RAM. Incase of power failure, the controller would simply signal the modem to retreive a fresh copy of the message. This meets all my requirements. The message is supposed to change every 15-30 minutes anyhow so protecting it through non-volatile memory is of little use.