THE TIME OF RECORD IS 4 HOUR.
To record sound for 4 hours and store it you will space no less than several ten's of MB's. Think of compact flash cards or a hard-disk for storing the recorded sound if you are planning to store good quality sound.
HOW CAN I DETERMIN DATE AND TIME OF MESSAGE?
Use a RTC and fetch the time from RTC when you get a call and store the time of call along with the phone number in some memory device.
CALLER ID
for Implementing a caller ID you need to know the modulation that your phone company is using for sending you the phone number of the caller. In some areas FSK is used where as in some other areas DTMF is used.

Regards,
Prahlad Purohit