Most people think that they need WiFi or 3G/4G connection for accessing the Internet on tablet devices.
The latest Android kernels have drivers for popular LAN controllers. This means that you can use a wired LAN connection to bring Internet to an Android tablet. Also, Android tablets now support USB host function. Most tablets provide a USB host adapter cable allowing you to connect a USB keyboard, USB mouse, or even a 3G USB modem/dongle.
Taking advantage of both features, you can use a USB LAN adapter with your smartphone or tablet.
I found a LAN adapter going by the name of Devante USB Ethernet Adapter at Infibeam.com costing Rs. 379.
When you are using the wired LAN connection, you can switch of WiFi and Mobile Networks. You can switch off both off them in shot by using the Airplane mode. The LAN connection will continue to function in Airplane mode! And, of course, you need to switch off the WiFi on your router. Most routers come with a panel of LAN ports to which you can use RJ-45 cables and use with your laptop/desktop. Now, with this adapter, you can connect your tablets and smartphones too. To top it all, the wired connection will be faster than your WiFi and 3g/4g connection.
PS: Devante is not really the name of the LAN adapter. They have just imported a generic no-name version from China and put their label. I checked the electronic label and it was Kontron (Industrial Computer Source). ICS was a famous label several years ago but the name is no longer trademark. Kontron has inherited the assets of the original company. ICS is now being used by a legion of Chinese companies manufacturing such generic products. The funny thing about this device is that they have not only used the ICS name, they have also swiped the Kontron name. The real Kontron company has no relation with this product!