elros34, not so useful other than qmegaphone uses FMtx and it might be neat to be able to add RDS to something you are doing.
Best application would be if you are doing community pirate radio and using the N900 as your initial signal generator and feeding it to a preamp and then say a 10-100watt amplifier and wire dipole or j-pole to the local area. But that is more an application for FMtx where you would want to have something flash over RDS as you transmit.