Need some help with a ECS that I am networking to a asterisk voip system over SIP. Anyone out
there done this?

Not your normal kind of set-up to be sure. Are you trying to use SIP trunks or stations at the ECS end?

In the old days we would use trunk at one end and single line extensions at the other. Realy not sure how to handle SIP. I was told that it has been done. Any ideas on this? I thought I would give it a go before calling Icon techs.

I've never tried using Peer/IP Authenticated SIP trunks on an ICON- done it many times with other system, though. Treat each end like a trunk and build your inbound and outbound routes as needed, may work out without too much trouble....or.....it could end up being a soup sandwich.