Says here
http://www.gsmarena.com/celkon_a40-6000.php WLAN Wi-Fi 802.11 b/g/n, Wi-Fi hotspot - Which means you need to go through your Android options and turn on hotspot, which makes your phone broadcast like Starbucks as a free wifi location for your PC devices to use. So instead of a WIRED (USB tethering) your using the WIFI to access the Phone's 3G/4G/etc. mobility options. Again you will need to check with your provider to see what they may CAP you on (MB per minute / per month limitations) because computers are doing ALOT of stuff (getting Windows updates, getting Antivirus Updates, checking your Chrome Apps, etc.)