thanks! this worked pretty well,now i can use WA on both devices with the same database and without re-registering. I only had to change the Android-UID of the app on the 2. device to the same one like on the 1. device.
the only strange thing is: i don't see my contacts anymore, but i'm not sure if this has to do with my mounting or with U11, as it was on the same day...