If you are in a foreign country, away from home, staying at a hotel, chances are you have horrible data roaming. Whether it is speed or cost, you want to get connected to a wifi hotspot as soon as possible.
Security problems aside, one of the issues with paid (or given as a pre-paid voucher to staying guests) wifi is that the system has some form of access controls. Most often your browser will get hijacked and taken to the log-in page. When you authenticate, the hotspot associates your MAC address with the credentials you supplied, and you are free to browse the internet.
Well, what happens if this association is permanent? I.e. once you log in with your computer, only that computer can use the hotspot. What about your phone? What about other devices? In such case, you have purchased internet access, but the access is restricted to one appliance, instead of one person.
There may be terms and conditions which you could violate by bypassing the restriction. Read them and see if you're allowed to connect other devices.
Meh. So how could we get around it?
Solution: share internet from this device.
So you got internet on your phone. Good. Share this access via cable or bluetooth (or wifi, perhaps) with your other devices. Problem solved! Quick and easy, if your phone supports it.
You could do this with your laptop as well, but you would probably need an external wireless network card as well.
Solution: use the same MAC address.
Note the MAC address of your phone, and then associate the account with your phone. When you want to use your laptop, simply change the MAC of your wireless interface to that of your phone. Disconnect your phone before you connect your laptop.
On Linux, you would run something like "sudo ifconfig wlan0 hw ether aa:bb:cc:dd:ee:ff", where wlan0 is your wireless interface and the a-f is the MAC of your phone.