First of all think in future expansion, if remote offices start growing you can start thinking in local Voice Gateways and SRST in remote offices.
Also select a platform that fits your current and future requirements, if using Cat 6500, I can recommend you CMM Module in order to have multiple T1s.
Make sure LAN|WAN QoS is properly defined.
Check out this:
www.cisco.com/go/srnd
Look for CallManager Design Web Page or you may open a case with PDI Team.