If you put your cable modem in standby (paused internet) your iPhone hangs
Apps that use the internet app store, cydia, facebook, etc... can appear hung if you pause your cable modem & run a wifi router. I think it's because each http request tries wi-fi, cable modem fails request, and has to switch to 3g. Since the router appears to be functional and the signal is strong I think it has to wait while constantly switching back & forth.
I sometimes pause the cable modem for my Cox connection and I forgot to unpause it. While it was paused it seemed like my iPhone was hanging every other app.
If wi-fi was off this didn't happen. That's my guess.