She is supposed to .. before transmitting .. how else would she (or
anyone) know if there is someone else using the frequency?

The whole purpose of setting up the radios with PL encode and decode is so you
don't hear the other users of the frequency. Once the mic is off the hook, it
makes that feature moot. Years ago, our volunteer ambulance shared a frequency
with a bus company. We'd take the mic off the hook to call dispatch and we'd
hear things like "Linda! You forgot to pick up little Jonny this morning. His
mother is very mad." Of course they were using a PL encode/decode, but
apparently it didn't open when they lifted their mics, so they never heard us.

Ham radio is different .. if a repeater needs a tone for access it is to
keep distant users of a similar (or same) frequency repeater from
accessing your local repeater unintentially. It is not to keep different
users of the same repeater from hearing each other.

We're talking on simplex GMRS freqs, not repeaters. There aren't any local
repeaters for us.
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
73! de Andy KC2SSB - WPYI880 (GMRS)
Beachwood, NJ USA! Grid FM29vw
http://vhfradiobuff.tripod.com