maybe try soundforge chicken vnc ?
if you can get it to load up on your iphone,, then you need to activate ALL your imac remote sharing (in your imac system preferences) and CHECK all the options in the options tab.
and make a note of the imacs IP. (a numerical number separated by full-stops).
and then you enter the IP number into your phones Chicken software.
if the VNC Chicken software doesnt work on your phone,, then search for another VNC App.
at a very least, you can access it from any computer in the world.
if you access from a PC, then you will need to use U-VNC (ultra VNC) to view your home imac.
if you access from a Mac, then you can download the above-mentioned Chicken VNC software