a. Configure AAR groups, prefixes as required
b. Enable AAR service parameter (set it to true)
c. Apply AAR groups to lines, gateways, voice mail ports etc
d. Apply locations to phones, gateways, voice mail ports
e. Apply AAR CSS to phones and gateways
f. Make sure that you have appropriately set the external phone number mask. In AAR group prefix settings use only 91 or 9 depending upon whether its a Local or LD.
This assumes that Locations, Route pattern and a CSS for use by AAR, have already been defined