I just tried this in several different ways.
I don't quite experience the same issue. Basically if I get a second call coming in while I'm on a call, I can answer that second call - but I have no way of going back to the first call! What's funny is if I end the call from my cell phone, the first call appears to call me back and starts up that call again - however the caller on the other end didn't do anything. (I work on VoIP phones for a living, so I have just a few lines/phones at my disposal
).
So call waiting definitely needs some work, but I don't experience the same issues you guys do.
I'm on FRX04 with the newest cam test stuff. I'd venture to bet 1253 is the same tho.