I have a 3G phone which can call back to the 3G camera at home. Bought from PCCW when my first girl was borned. I also have a network camera bought from 鴨"療"街 which I can watch (no sound) from work.
I don't know whether it is legal or not but both camera is in the lounge. I also told my Indonesian maid about it. I told her a I watch BB anytime using the camera and ask her not to move it.
I think it should be ok. Just don't install in the room or toilet as you might be caught for intruding privacy..