There are basically 4 major online casino application providers and the licensing models vary. Typically there is a recurrling license fee plus royalties.
http://www.bossmedia.se/
http://www.worldgamingplc.co.uk/
http://www.microgaming.com
http://www.cryptologic.com/
You can also go the sublicensing route.
http://owncasinos.com/