As soon as Apple released the iPhone OS 3.0 to developers, and new functions has been capturing a lot of attention: Internet Tethering. This function is quite simple: it turns your iPhone into a 3G modem, so you can browse the web from your computer via your iPhone.
Of course carriers will not allow such usage for free as it uses 3G bandwidth on their network. Well, you could argue that having an iPhone-bundled data subscription plan should give you the right to use the internet tethering function as part of your plan. Well, no; it is considered as "data', but it is not the same "data". Some users quickly developed hacks to bypass restrictions applied by carriers. It is relatively simple, however it is not clean and carriers can track your "illegal" data consumption via internet tethering.
In most EU countries unlimited data is often "limited" to 1 GB data transfer
