Or rather, DON'T hack any paid WiFi hotspots, as that would be bad...
Also, don't turn your WiFi card off and then back on again after the hack to rectify any MAC address conflicts that might arise.
The commands are:
ifconfig en1 | grep ether
sudo ifconfig en1 ether [mac address to spoof]
Note that the term "MAC address" has nothing to do with Macintosh computers. All computers, including Windows machines, have MAC addresses. This address is unique to your computer, but can be changed in software. The practice of copying someone else's MAC address is referred to as "spoofing". Spoofing a MAC address can get you through any MAC address filter, like the ones used by public WiFi hotspots.