Usually when you purchase a prepaid cell phone from any carriers, for example T-Moblie they are locked to that carrier in particular. This means that you can only use the cell phone with their services. But if you want to travel for instance and you don't want to roam, this is where you will find trouble. You will have to unlock the cell phone in order to use other carrier's sim cards. In this way you can just buy a prepaid sim card in the country you are visiting and be reachable.

Steps to unlock your cell phone

1. The first option is always contacting your service provider and ask for an unlock code. Most of the time if you have been a client for a ling time and spent a good amount of credits with their services they will provide you with the unlock code. This can happen right away or can have a delay of a couple of days. So don't wait until you are ready to travel to request the unlock code.
2. Download a program that can calculate the unlock code. Programs are available freely at some sites and at some sites you may have to pay a small fee. Most of the time this is a calculator program for Nokia, Panasonic, Samsung and Siemens. Click on the links to download the unlock calculator or you can use alternativelly the online calculator.
   
3. Now it is time to get ther Serial number of the cell phone, known as your IMEI number. This can be done by either removing the back cover of your cell phone and looking under the battery, or simply by keying in *#06# onto your cell phone. You should get a 15 digits numbers answer. It should look like: 354223035488512.
4. Using the program you have just downloaded, Selct the brand Nokia, enter the IMEI number in the program's IMEI table. Select the Country where the cellphone was purchased. Select the carrier from which the cell phone was purchased. Now Finally click on calculate.
5. Now it is time to turn off the phone and remove the sim card. Put the battery back in and then power back on.
   
6. You will see a message "Insert SIM Card". Enter all of the numbers you got back from the program, including the # symbols starting with number 1. If this fails continue to number 7 and upwards (6,5,4 etc.). The code will look something like this: #pw+356763556617464+7#. To get a 'p' press * 3 times, to get w '+' press * 4 times, to get a 'w' press the * 2 times.
7. Once you have finished entering a code that works you should see a message that says "Restriction off" If not, then try entering another code. Remember you only have 5 chances to insert the correct unlock code. After this you will get the message "Cannot undo restrictions". Automatically this means the phone is "hard-locked" and cannot be unlocked by code anymore. Now you have to take the cell phone to a service center in order to be unlocked.

* Tips

• For some models, such as the E51, you may unlock them simply by updating the phone's firmware using the Nokia PC Suite.
• If for any reasons you need to factory format a nokia phone you need the code *#7370# (this only works on newer models).
• You can purchase an unlock code from a website http://www.unlockitnow.com
• They can unlock your cell phone to work with any other GSM network world wide for a small fee and Guarantee their results.