AT&T feature module 2 Switch, your tones will be different, If you hear this type of tone

The MERLIN II system also provides you with the following tones on your
voice terminal, unless you have a behind-switch system, so that you know
		.
	immediately what kind of call you are receiving. If your system is behind a
	switch, your tones will be different.
	If you hear this type of tone:		You are receiving this kind of call:
	One short and one long ring		Transferred Call
	A beep and then a voice announcement		Intercom Call with Voice
	through your voice terminal speaker		Announcement
	A beep and then a voice announcement		Transfer Call with Voice Announcement
	through your voice terminal before you
	receive a transferred call
	A beep (The 7406 voice terminal has a		Manual Signaling
	timed beep; on the analog voice
	terminals the beep lasts for as long as
	you hold down the Manual Signaling
	button)
	Two short and one long ring		Ringing Intercom Call
	One long ring		Outside Call

CONSIDERATIONS	● You can program your voice terminal with a ringing pattern that is
	different from the ringing sound of nearby voice terminals. (See
	“Personalized Ringing. ” )
	● People with the 7406 voice terminal can place both ringing and announced
	intercom calls, but can receive only ringing intercom calls. When someone
	in the MERLIN II system places an announced intercom call to a 7406
	voice terminal, the call automatically becomes a ringing intercom call.

MERLIN II System Features 2-159