Unable to connect to public wifi that requires log in

I have an Iphone 4s. Got it last October. It connects to my wifi at home fine. Connects to other home networks and public networks fine too, as long as there is no log in page required for subscription. If there is a log in page required to join a public network, the phone finds the network and I get the connection signal in the top left corner, then it seems to try and open the log in page but it gets hung up there ALL THE TIME. It does this at several different public places now. Restarting, resetting network settings, reset all settings on phone but nothing fixed it. My daughter has a 4s, my wife a 3g. They have no problems connecting when they are in the same public places. I also had no problem when I was using my 3g in theses same places. I have a friend/co-worker who has a 4s, and he has the same problem as I. I have found a way around it, perhaps suggested by someone here? If I turn my phone to airplane mode, then turn my wifi on, it will load the log in page for the public wifi and I can connect. Then turn airplane mode back off and it will stay connected to wifi. This is inconvenient, especially because in several of these public wifi places you have to renew the lease frequently so I have to go through those steps again. Any suggestions or ideas?