In order to use an O2 SIM card with a Tesco phone, you have to unlock the Tesco phone first. Cell phone providers lock their phones to keep users from switching their mobile phone service needs to other competitors. However, after a year, Tesco will provide you with the unlock code for free. If you can't wait that long, you can turn to an online company that specialises in providing unlock codes for cell phones.
Contact Tesco for the unlock code if you want to use your Tesco phone with another network. Tesco will provide the unlock code after twelve months of using the phone with its original SIM card.
Text "*#06#" to get the IMEI number. The IMEI number is a unique code for your phone that determines the unlock code.
Slide off the battery cover and remove the battery. Take the original SIM card out of the phone. Do not yet insert the new O2 SIM card. Insert the battery and slide on the battery cover. Press "Power" to turn on the phone.
Go to a company that provides unlock codes if you are within the twelve month usage agreement with Tesco, and so cannot obtain the unlock code from them.
Go to the main screen of your phone and enter the unlock code provided to you by either Tesco or the phone unlocking service.
Remove the back door of the battery and remove the battery. Insert the O2 SIM card and replace the battery. Slide the back cover over the battery compartment.
Press "Power" to start up the phone. The phone will be unlocked and can be used with any SIM card.