I believe my 'voice line' is being tapped [the line feeds through the
> 'opponents' switchboard].
Who is this "opponent?" If it's an LEA, you've been PWNED. CALEA requirements dictate that all your communications be stored in a massive bucket, where the LEA can expend all the time and technology necessary to decode your communications. Not even encryption will prevent your messages from being read, if the LEA really want to read them bad enough.