I recently had a project where we were moving our hosting to 1&1.  This included moving our phpBB database to the new host.

Some of this was based on the KB article at phpbb.com .

Somethings to note:

1. Before exporting the database, change the default board to prosilver.
2. On 1&1 hosting, the database user name starts with dbo and is not exactly the same as the database name as it is with some hosts.
3. Use BigDump to populate the database.  Otherwise, the phpAdmin times out and does not populate all the tables.
4. BigDump only processes .sql and .gz files.  To get the .sql file into 1&1, zip it and upload it.  Then unzip it.
5. If the phpBB version is more current than the database, download the new phpBB version from phpBB. Unzip into a new folder.  Rezip the install folder and upload to the phpBB folder on the new host.  Unzip it there.