Assuming you completed your contract term with the original carrier, you should go to them to unlock it. Myself, I only get unlocked devices. I had a Nokia that I wanted to unlock and tried one of the online services - it didn't work. Fortunately, I was only out about $10-20 USD for the effort. In the USA these days, I think that the carriers have to unlock the phone/modem if you have fulfilled your original contract that subsidized the device.
its simple to unlock your huawei EC156 modem using unlock codes.you can ask for the network provider to which it is locked to or else you can go for online providers such as [snipped] here all you need to do is just give your IMEI number,country/network to them and they'll give you code to unlock your huawei modem.its easy try it out.