Looking for any advice here, a bit wet behind the ears on this one...

Looking at a large site with about 4500 Shoretel users spread out across several separate systems, and a couple of dozen legacy PBX sites that have a variety of systems.

Plan is to slowly implement Cisco at the legacy sites and have them be able to 5 digit dial the main Shoretel site.

My first thought is SIP trunks between sites (MPLS is in place already).

Any other (easier) ways of doing this?

Where could I gen some info on the Shoretel side of this setup?

The entire site will eventually be Cisco, but the the complete takeover of the Shoretel could take 5-7 years.

D