This is a belated reply, but for iOS - when it was available, VLC could do RTSP streams. I was able to get video and sound from my ip netcams. Unfortunately, it is no longer available on the iTunes store.
I did find another app that handles RTSP in iOS, OPlayer. There is a Lite version that is free with ads and a paid version. I found the user interface difficult to understand, but it did handle the RTSP streams from my trendnet IP422W and LTS LTCIP830MV.
You may also want to check the iTunes store to see if your netcam's manufacturer has an app. Trendnet recently created an app for their netcams that does video with audio.
Of course, I am looking forward to when iCam has more support for audio.