i cant confirm this for the iPhone, but it works on iTouch:
install term vt-100

then tap on term vt-100


and enter the following:
Code:
ifconfig en0 ether XX:XX:XX:XX:XX:XX
"X" Stand for the MAC Adress you would like to use


Notes:
This will be ineffective after you restart the iphone/itouch.

THE NEW MAC ADRESS HAPPENS NOT TO SHOW UP IN THE ABOUT SECTION

just look into ur routers connected devices and it will show u that you have changed the MAC.

thumbs up if my guide helped