Connect Sierra Wireless Modem to computer, wait till it is recognized by PC. Afterwards launch DC-unlocker ICERA unlocker client
Open User Account data tab, enter your username and password that you received after credits purchase. Click "Check account status". (you can buy credits here www.dc-unlocker.com/buy) If DC-Unlocker/Vygis/Rocker/Infinity dongle is connected, do not enter username and password, only click "Check Account status"
Click "Detect device" button, wait for the program to detect modem
Note: If modem was not detected make sure you have installed drivers for it. Drivers here
Click on Unlock tab and press "Unlock" button, wait for the device to be unlocked.
Reconnect modem to pc, now you can use it with other provider's cards