Since a couple of days the SP2 for Microsoft Exchange is available for download on the Microsoft Website. With the release of SP2 it will be possible to migrate to Exchange Server 2010 in the future.
I already did some upgrades to SP2. There is one important thing you should know. If you are using the Unified Messaging role with language packs different to the english one you’ll have to deinstall them before the upgrade to SP2. After the upgrade you can install them again…Oh wait, you need the correct version of the language packs. At the moment there are no SP2 language packs available. So you will have to stay with SP1 or upgrade to SP2 and stay by the english builtin language pack and install your language as soon as it gets published on the Microsoft website: http://technet.microsoft.com/en-us/exchange/bb330845.aspx At the moment there is no release date published.