Used by the routines at 75F6, 76FA, 776F, 77D3 and 7A0C.

Bit(s)	Meaning if set
0	Unused
1	The telephone call is finished (disconnected)
2,3	Unused
4	A digit is being dialled
5	The destination telephone is ringing
6	Sam must give a name in response to 'WHO'S THERE?'
7	Sam has picked up a ringing telephone