asterisk users - Jun 2004 - CFDA from cell phone to SIP line in Asterisk PBX

I have something I'd like to try, but don't know if enough information
would be delivered to Asterisk to make it work.

I have a cell phone that I would like to forward on "Don't Answer"
to an
iConnect phone number that is then delivered SIP to my Asterisk PBX.

I'd like to be able to route the call when it is received by Asterisk
based on the number that the caller dialed, ie, the cell phone number.

So, my question is, of all the ANIs delivered to Asterisk by a SIP call,
would the number orignally dialed be included in the mix?

If so, what variable (if any) does Asterisk assign to it?

TIA

-- Greg --