Nokia C5-03 unlocked cell phones generally work on all GSM networks. A Nokia C5-03 that is locked to a single phone carrier and uses a SIM card will need an unlock code in order to remove the SIM lock that comes on most SIM devices by default. If your Nokia C5-03 has a SIM lock on it, then it will prevent you from using the mobile phone with any other carriers.
I would first recommend you try getting a Nokia C5-03 unlock code by calling up your current phone carrier. In exchange, they will need your Nokia C5-03′s IMEI number. Your IMEI number is unique to your mobile device and the Nokia unlock code will be calculated using it. You can get the IMEI number on your Nokia C5-03 simply by typing *#06# and hitting the enter or send button. If you do not currently have a carrier or cannot get a free unlock code, then I would reccomend trying some of the unlock code websites that I have reviewed below.
Once you have your unlock code, you can begin the Nokia C5-03 unlocking steps below.
How To Unlock A Nokia C5-03 (SIM Unlock)
1. Power ON your Nokia mobile phone without your SIM card.
2. Now type: #PW+CODE+1# (Where CODE is your Nokia unlock code)
3. Your phone should now show “SIM Restriction Off” and is unlocked.
Note: You must press the * key several times to get the characters for ‘P’ and ‘W’.