Maybe it's because most punters don't themselves (due to age) ... but ... why do agencies never check their email, Twitter, Facebook, ...?
For me, it's easier to contact them in that way... rather than having to walk out of the office, out of the building - and a decent walk away from the building - before making a phone call... which, for any of my work colleagues driving past, can look very suspicious anyway... it's especially annoying when the agency phone is busy and I then have to wait 5-20 minutes before I can get through.
Much, much easier if I could rely on them checking their emails..............
Another idea: similar to the Apple Shop app on iPhone, how about having something like that for parlours/brothels where it auto-detects that you're nearby and pops up a message telling you who is available and when? ... Like Apple's "Genius Bar" but they could call it a "Fishbowl of Girls"
nb. I am, of course, being sarcastic on that last point ... just as I am in my digs at oldies... I realise how grumpy you can all get!