asterisk users - Sep 2004 - design check

Hey Guys,

I am getting ready to implement Asterisk for my company. We plan on housing
an asterisk server at a local termination provider and have another here in
the office. The two communicate via IAX. Looking something like...

PSTN
 |
PROVIDER
 | (PRI)
Asterisk
 | (IAX over the Internet)
Asterisk
 |
SIP Users


The idea here is that the local sip phones can communicate with the local
Asterisk server and cut down on network traffic across our corporate
internet connection.

Also, I would like users who are not in the office (travel, home office,
etc.) to be able to connect directly to the Asterisk box at the provider.
This will further cut down on local traffic.

Finally, when a call comes into the Asterisk box at the provider, I would
like that box to check if the requested user is logged in down in the
office, and if not don't send the call across the internet. Instead, see is
the person is logged in directly. If the user is not present at all, try a
cell phone or send to VM. Again, this would limit traffic across our
corporate internet connection.

Has anyone had any experience with this type of implementation?

Does this make sense, or am I making things to complicated?

Is this configuration and functionality possible?

Any other comments or suggestions that may help me accomplish my goal of
providing a telecom infrastructure to a company of 20 software engineers who
are mostly in the office but could be anywhere.

Thanks a bunch guys.

~chris