Note: Its strongly recommended to migrate LCS 2003 setup to LCS 2005 sp1 before migrating to OCS 2007. Still we have some workaround to acheive the same.
I recently encountered a situation where the customer had already installed OCS 2007 in his LCS 2003 Active Directory. Now they didnt have any other option than searching for workaround to move their users directly from LCS 2003 to OCS 2007.
Main problem behind direct migration from LCS 2003 to OCS 2007 is that you dont have any tool to migrate users from LCS 2003 to OCS 2007.
If you have LCS 2005 sp1 setup, the LCS server will apear in OCS 2007 console. You can see LCS users in OCS 2007 console. You can right click the LCS users and select to move the users to OCS 2007. We dont have this luxury with LCS 2003 setup.
You have only one option to manually changing home server of a user from LCS 2003 to OCS 2007. If you do this you will loose the contact list of this user.
So the solution includes taking backup of the contact list from LCS 2003 and importing it to the OCS 2007 database. Sequence will follow as this:
a) Take backup of LCS 2003 users contact list using OCS 2007 dbimpexp.exe tool.
b) Change Home server FQDN from LCS 2003 to OCS 2007 FQDN. You need to do it either manually or using any script.
c) Restore the contact list to the OCS 2007 database using dbimpexp.exe tool of OCS 2007.
This operation is not supported by Microsoft and involves more manual operations... but still you can achive it!
Move Users to a Different Live Communications Server or Pool
How to export and import contact list (dbimpexp.exe)