Starting to see lots of questions on forums about setting up a hosted Exchange 2010 system.
Well to be supported, you are going to have to wait 12 months.
"Hosting in Exchange 2010 will be supported approximately twelve months after the release of Exchange 2010."
http://www.microsoft.com/hosting/solutions/hostedmessaging.mspx
MS Exchange Server, Exchange 2010
MS Exchange Server, Exchange 2010