covert@covert.enet.dec.com (John R. Covert 01-Apr-1991 1615) (04/02/91)
> The M was added when modular hardware was installed.
Not so. The "M" indicates that A-lead control is provided.
Internally, the set is wired so that the switchhook, when lifted,
makes a contact closure between the Black and Yellow wires, in order
to provide control if the station has an appearance on a key system.
/john