Question about tethering... does it "share" the IP address of the modem (iPhone) with the device it's tethering (laptop)? ie., does the iPhone give the laptop its IP, or does the laptop count as a separate device on the network, and obtain a unique address?
If it has a unique address and thus a separate device, I wonder why you can bypass the network's login restrictions. If it has the same address, I could see why it would behave that way.