Usually, 'unlimited' means 'limited but we won't tell you the limit'. If you'd download fullspeed (3.5 mbit) on 3G 24/7 you'd burn about 886 gbit (110 GB) a month. Try it out for fun and profit, but most ISPs will either: 1) contract you with a 'special offer' or 2) cap the crap out of you. You've been warned.