Cell phone unlocking allows you to remove network restrictions imposed by your network carrier to discourage you from moving to another carrier. If your cell phone's SIM card has been locked to a particular GSM network, you have a number of options to unlock it.
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Call the customer service department of your network service provider and request a SIM unlock code for your cell phone. To get your carrier to provide you with the code, your account must be in good standing.
Find a free unlock code online. Websites like Hyfeno, Peters1, Nokia Free, GSM Liberty and Unlock it Free (see resources for links) provide free unlock codes for a number of Nokia, Samsung and LG handsets as of 2010. If you find your the unlock code for your cellphone on any of these websites, note it down. You will get the unlocking instructions along with the code
If your phone doesn't have any free unlocking solutions, see the next step.
Give your handset's IMEI code to a pay service like Global Unlock, Unlock All Cellular or Unlock it Now. These pay sites can generate unlock codes for almost every handset based on its unique International Mobile Equipment Identity (IMEI) number. Depending on the cell phone model and the carriers its locked to, the price will vary roughly between $7.99 and $46, as of 2010. After you pay through your credit card, the code will be sent to you in an e-mail.