freewifi.sh

#!/bin/bash
: '
	Change your mac address on a MacBook
	Can be used for free wifi on airports or train stations =)

	$ chmod +x freewifi.sh
	$ ./freewifi.sh
'
interface=en1 # en0 for cable & en1 for wifi

oe=$(ifconfig $interface | grep ether) # save old ether output
a=$(openssl rand -hex 6 | sed 's/\(..\)/\1:/g; s/.$//') # generate new mac address
sudo ifconfig $interface ether $a # change mac address
ne=$(ifconfig $interface | grep ether) # get old ether output

if [ "$oe" != "$ne" ] # check if mac address is changed.
then
	echo "Mac address changed."
fi

Mer info:
http://rasmuskjellberg.se/surfa-gratis-obegransat-pa-flygplatser-eller-andra-begransade-natverk/