Your carrier may offer you unlimited 3G, LTE data service as long as its used on the phone, but the moment you try tethering it your PC / laptop, they start charging for it or worse, limit the data.
Koushik dutta, a developer, has figured out a way to bypass this Tether detection used by AT&T, sprint, and others. He released an app which offers user “undetectable tethering” and the app is called ClockworkMod Tether Alpha.
ClockworkMod Tether doesn’t need your Android phone to be rooted, and allows Windows, Mac and Linux users to utilize the 3G or 4G LTE connection of an Android as if it were a proxy, as opposed to a Wifi/ usb access point router. Technically, it actually spoof carriers checking for the TTL (Time To Live) data coming from a desktop, which is unique for every OS. It modifies the IP packets transferring from PC and changes the TTL values in the TCP/IP header.
The computer app installs a virtual connection which understands how to communicate with the proxy on the phone.
However, app will self-destruct on 7th January 2012 in order to encourage users to purchase the paid the version. Bluetooth tethering is also in the pipeline.
Go ahead and try the Alpha version from here on Google+ post.