I actually had more problems to turn on the light at my desk to write this than putting the N900 with the BH-905 and my TV to tests

I am running v47 of power-kernel clocked to max 850MHz and the CSSUpdates on my device.

I use the TVout control widget to tune the output of the N900 video to the TV. I connect the BH-905 through bluezwitch widget with the N900 and started a video, which did just what you expect: Transfer the sound to the BH-905 fine.
Next i phoned home, the sound switched to the telephony application and the video stuttered a little, possibly because of too much work for the CPU, but kept playing on the TV screen, while the N900 was showing the telephony dial pad.
Next i called the N900 from the land-line, and again the video just stuttered, but kept playing on the TV while the N900 showed the incoming call.

This phone and the applications the developers had delivered are just awesome!