A recently updated file-manager app for iPhone has stealthily brought in the ability to tether your smartphone's 3G data to a computer without having to sign up for expensive mobile hotspot plans.
The £1.49 QuasiDisk app for iPhone is essentially a tool which enables you to read or play a host of different media files on the go, but a few tweaks here and there allow free tethering to Mac or PC computers.
Apps which offer free tethering are usually dispatched from the App Store very rapidly, so it might be a good idea to get this app while the going is good and perform the following instructions.
First you'll need to create an ad hoc network on your laptop (Mac / Windows instructions) before starting QuasiDisk's FTP server on port 5100 and writing down the full server address. Then you can connect your laptop to the FTP server via proxy.
There are detailed instructions on exactly how to configure the workaround in the video below posted on 9to5Mac. If you act fast, this could save you a fortune in data plans.