I would like to make sure you know, there is a "dirty" route to migrate to the UBB... PHPBB can import just about any product, so you can import into PHPBB then import to the UBB from there...
I can't vouch for what will be imported (as it's a filthy process to import), and I know there are still a couple of bugs in the phpbb importer; but it's a decent route of how to get migrated immediately.