What is tethering ?
Tethering refers to using an internet-capable mobile phone as a modem to share its internet access with other devices, such as laptops or PCs. This sharing can be accomplished over Wi-Fi, Bluetooth, or by physical connection using a cable.
In the case of tethering over Wi-Fi, the mobile phone acts as a portable router and the feature is aslo called a mobile hotspot.
Many mobile phones, including Windows Phone 7 (from version 7.5 Mango), Android (from version 2.2 Froyo), and iOS (4.3 or higher) offer tethered Intnernet access. The feature is sometimes disabled, or requires extra monthly fees by operators to reduce strain on their networks.