Select the "Use Metal Gear" option, then use the Videophone. Dial "34-5678" to view a message from one of the game's programmers. For other messages, dial the following numbers.

41-6766 (Jeremy Blaustein)
34-5678 (Taeko Hayasaka )
44-3723 (Hideo Inamura)
33-3333 (Satoshi Kushibuchi)
84-6736 (Keizo Nakamura)
79-6641 (Moai Sasaki)
44-6454 (Mitsuhiro Togo)