Cross Platform Event Notification
Maybe have a look at www.pubnub.com .. its commercial, but lets you send 5 million messages a month for free. Essentially it lets you create a named channel, and have X number of clients connect to it and send messages back and forth. 
Using one of these services would of course require you to write a client to distribute to your users (in your language of choice) and tie's you in somewhat (shouldn't really be a problem as you could swap in some other solution later if they go under or whatever.) 
The upside would be, very good x-platform support and a very clean API, infrastructure taken care of for you (for example clients can still connect the the channel even if your asterisk box is down or whatever)
(and no, I don't work for pubnub! but it seems like a no-brainer to use it with the 5mil messages free deal!)
I hope you guys can spare a moment with some ideas on how to develop my idea.
I have an Asterisk-based telephone switch . When an incoming call is arriving, I can make sure the server runs an external script of any language.
Here comes my development work. I would like to notify a group of listening clients about the call, and probably open a browser page on their computer.
What kind of approach would you take for this sort of server-based push notification? (with no iPhone involved)
I am open to any language.
Thanks