You have to follow these simple steps in order to get your Huawei E303 Modem unlocked which is permanently locked only with Customized Firmware (both Hilink and Non-Hilink Modems):
1. You can get instant & free online firmware flash code from here
2. After opening the above link Put the IMEI and get the FLASH code that we are going to use them as a PASSWORD.
3. Download HUAWEI E303 firmware update from here
4. Unzip the file and make sure the modem is connected and it has been installed with the SIM card inside it.
5. Quit the dashboard if its open and run the update, wait and when it ask you for the PASSWORD input the FLASH CODE you got from step 1.. Wait for about 3 min and your modem will be unlocked PERMANENTLY.