I got a new router that is ridiculously good and has exceptional range. A side effect of this is when I go for a walk, I have to be walking for at least 5-6 minutes at a brisk pace, before the WiFi connection on my iPhone 4S is lost. Basically, beyond 100 yards/meters there will be 1 WiFi bar and it will be all but unusable (e.g. Web Browser times out, Siri doesn't work, etc...). Under these conditions, I'd rather use 3G (ahem, 4G).
Is there a way to automatically disconnect from the WiFi when it gets down to 1 bar?