Hi crsCR and Russ,

CC-BY is not compatible with ODbL.

I try to summarize it:
CC-BY allows you to use it as long as you refer the source. eg: “source geonames.org

ODbL requires you to state the source, eg “data: ODbL OpenStreetMap.org and contributors”

did you notice it already? you can’t force ODbL users to add “and geonames.org”. And leaving it away violates the geonames license.
So it is not a valid source for us.

One solution would be to get a special permission for use in openstreetmap and have the attribution in the wiki, see here for some examples:
http://www.openstreetmap.org/copyright
http://wiki.openstreetmap.org/wiki/Contributors

Stephan