The best way to obtain free mobile internet is to find a place that offers "free wifi". There are plenty of restaurants, libraries, and coffee shops that provide this service, and all you need to do is to be within range of their wireless network.
You can use services like Foursquare to find places that offer wifi near you.
- Some home internet providers allow their customers to have access to free wifi. You could sign up with one of these providers for your home broadband.
- Likewise, some mobile phone providers will give their users free wifi, but you really should check what else you get as part of the package. Just because something is classed as free doesn't mean it actually is. If you're paying $30 per month for your phone, but only want the free wifi, you're actually paying $30 per month for your wifi.
Ultimately, the best way to get free mobile internet is to find an establishment that offers it. There are some dodgy websites out there that will claim to teach you how to hack into someone else's wifi, but I wouldn't recommend trying to do this.