[Asterisk-Users] hint priority...how does it work?

[Sean Kennedy]

So, from what limited info I was able to find in the wiki, the hint 
priority should let another phone know when an extension is in use.  So 
if we had this...

exten => 1000,hint,SIP/101

when ext 1000 is dialed, SIP/101 can see it..somehow. 

how does this work, exactly?  Can anybody provide a bit of background 
and depth to this?

Thank you

Sena