[Asterisk-Users] Simultaneous ring internal extension and external phone number?

[Kevin P. Fleming]

I have a client who is looking at replacing their PBX, and I'm 
interested in putting together an Asterisk solution for them. One 
feature that would really, really get their attention is if I could do 
the "Vonage" thing, where if a PSTN caller dials a direct extension 
(coming in over PRI) both the user's deskset _and_ an external number 
(their cell phone) would ring, with either being able to answer the call.

Is there a way to do this with Asterisk? Based on my review of the 
handbook and parts of the wiki, it looks like it could be done quite 
easily in the dial plan. However, I have never installed Asterisk so I 
am quite clueless about what will actually work :-)