Now that I am at work, and have coffee in me and not beer, I will go through the problem I had with miCap and works wireless. Due to my skeptical ways, I will be semi vague for security purposes. On with it.
When I originally got miCap (pet name for it) I was able to access our public wifi. It allowed me into the public portal to agree to terms. I played a little bit on it, but wanted to see if I could access our private wifi. I got in the private no problem. But after that I never was able to get back on to our public. It did the same thing as I've read. It got an ip no problem (via dhcp) and acted like all was well. No browser, or ap could get a connection. The phone would not switch over to 3g to get info.
Armed with ip and mac address, my co-worker and I started to did through our monowall. ( He also has a cap that had no issues on public or private). We try tried reserving the ip for miCap, didn't work. We tried static ip, didn't work. I spent the morning completely wiping miCap to get it back to return worthy.
This was when I decided on last ditch effort.
Our ap's are cisco's that connect into monowall. I got into monowall and dug around. I found that with in the captive portal (how fitting) that the ip/mac associated with my phone hadn't checked in for 8 days. Even though I tried everyday. I deleted the entry to the phone there and suddenly my phone was getting access again.
Now I understand that this may not help everyone, because setups vary from place to place. But digging deeper into configurations at the access points may be what is needed. Do I think the phone had nothing to do with it? No, I think it helped aggravate the problem.
We have had problems with the Intel 3945abg chipsets with the same exact setup. That problem was fixed with driver updates on the laptops.
sorry for the long winded reply.