Question : Need to run Exchange 2007 in domain with trust

I am replacing SBS 2003 server with server 2008 in two seperate domains, which will be connected with a VPN tunnel. I need to have a full copy of Exchange 2008 in each location that includes users from both domains.
Will a trust work, or should I create a forest?

Answer : Need to run Exchange 2007 in domain with trust

No issues in that case you can have SCR on the local site as well or even you can have CCR for that .......