Will the DB scheme change?
It is possible that during the following development the open-xchange-groupware db scheme will change?
If yes, it is possible to migrate the existent data (calendar, contacts ...) to the new db scheme?
The first answer is a resounding YES. Of course the database schema will change.
The second answer is also a resounding YES. We're working on an update system that automatically migrates the data in your database to the current version, without you having to do anything. That's already in the OX:CE edition though we haven't gotten around to testing (or using, for that matter) it.
The development of a conversion tool is good news, but can you say anything about the time line of availibity?
Keep in mind that this update tool works for OX:CE only, so it will only work when upgrading an OX:CE to a later OX:CE from the CVS.
IIRC the handling is that the database is updated once you log into your account by the ox-server, so there is no extra tool, just a login message telling you, your database is being updated and urging you to drink a nice coffee in between (maybe not exactly like this). This is part of the current OX:CE already, if I'm not mistaken, though there are hardly any changes to the db schema at the moment (other than the table used to keep track of the db schema version that is added by the first update).