I beleive, based on what you are describing, you are looking for Tail-End Hop off. TEHO is the circumstance where a call is routed to the local gateway (router) where it is then passed out to the PSTN to be processed as a local call.
(Cisco Documentation)
Within a centralized call processing cluster with N sites, you can implement Tail-End Hop-Off (TEHO) using one of the following methods:
-TEHO with centralized failover
This method involves configuring a set of N route patterns in a global partition, with each pattern pointing to a route list that has the appropriate remote site route group as the first choice and the central site route group as the second choice.
-TEHO with local failover
This method involves configuring N sets of N route patterns in site-specific partitions, with each pattern pointing to a route list that has the appropriate remote site route group as the first choice and the local site route group as the second choice.
While the second approach allows for an optimal failover scenario when the remote gateway or the IP WAN is unavailable, it also introduces a high level of complexity into the dial plan because it requires a minimum of N2 route patterns and N2 route lists, as opposed to the N route patterns and N route lists needed with the first approach.
•When appropriate for your national numbering plan, you may configure an additional translation pattern at each site to catch local PSTN calls dialed as long-distance calls and to translate them into the proper abbreviated form. This translation pattern should be accessible only from phones located within the site. Such a configuration also helps simplify the AAR configuration (see Special Considerations for Sites Located Within the Same Local Dialing Area).
•Do not use the multilevel precedence and preemption (MLPP) feature to assign higher priority to emergency calls. An emergency-related call might not appear as such to the IP Telephony system, and you would risk terminating an existing emergency call to place another call to the main emergency service routing number. For example, an emergency situation might prompt someone to place a call to a regular ten-digit number to reach a medical professional. Preemption of this call would abort the ongoing emergency communication and could delay handling of the emergency. Also, incoming calls from emergency service personnel would be at risk of preemption by MLPP.
link to document:
http://www.cisco.com/en/US/docs/voice_ip_comm/cucm/srnd/4x/42dialpl.html#wp1043613
(I think you need a CCO login to access it).
