One of the thing to consider is which gateway potocol to use for the remote sites. H.323 is preffered, this is beacuse with MGCP, your signalling protocols will be transversing the WAN, which is not best practice.

Another thing is to use SRST for the remote routers so you can have resiliency.

Also, make sure you have a dedicated DHCP server in each remote site, as you dont want dhcp relay flying over the WAN.

Thats all I can think of for now

Hi Ashok,

Hope all is well! Just wanted to add this link to the great tips from my friend Deji. This contains many design ideas for your model;

Unified Communications Deployment Models

http://www.cisco.com/en/US/docs/voice_ip_comm/cucm/srnd/6x/models.html

Hope this helps!

Rob