Web Based Method To Determine If An IPhone Is Connected Via 3G Or Wifi

I'm in the process of building a webapp that allows users to view a video podcast. At present, the user can select whether they would like low or high bandwidth videos depending on

Solution 1:

You probably don't care about 3G vs WiFi as much as you do about bandwidth/roundtrip time.

I wonder if you can achieve this by not detecting 3G vs WiFi but by computing round-trip time using a browser script and using that to determine the fidelity of the user experience.