I believe this is a bonus or promotional item from TDK cassette tapes of that era. It is likely a very valuable item. It is unopened, but the box has some damage. Also, it is compatible with mobile phones and PHS of that time, but I have not tested its operation, and I cannot guarantee its operation as it is an old item. Originally, the keychain is supposed to light up when there is an incoming call. Please consider this with your understanding.