Not quite what you asked for, but mgetty sets the modem up to say "RING"
when the phone rings - it can then do a blocking read on the device.

--sjg

>Is there a neat way for a process to sleep until modem signal on the RI
>line is detected?  TIOCMGET will tell me whether the line is active now,
>but I would like the system to tell me when it is active, rather than
>having to repeatedly poll.