There are 2 different solutions you
could use.
The first uses the DNIS number to determine
which AAA server to use. That AAA server
could then download the IP pool that
you want used. You can read about it here:
http://www.cisco.com/univercd/cc/td/doc/product/software/ios120/120newft/120t/120t7/serdnis6.htm
The second solution uses Resource Pooling;
you configure a Customer Profile for a
particular DNIS; this profile would then have
a template associated with it, and this is
all controlled by the DNIS. You can read
about this feature here:
http://www/univercd/cc/td/doc/product/software/ios120/120newft/120t/120t7/rp1206ta.htm