Whether your SIM card is several years old and in need of replacement or you've purchased a phone recently that came with a new SIM card and you just want to switch, some degree of preparation is involved to ensure all of your contacts carry over. It is not difficult to move the contacts over to the new SIM card but it may take some time and effort depending on the circumstances involved.
Utilise a SIM card copier if available. GSM carriers like T-Mobile and AT&T supply many of their retail outlets with devices capable of moving data from one SIM card to another. They use this device for customers who have outdated SIM cards that need replacement. While this is the easiest solution, not all retail locations have SIM card copiers, so call ahead to confirm before visiting a store.
Copy contacts manually from your old SIM card into your phone's memory if a SIM copier is not available. This is generally done by hitting "Menu," "Phonebook," and then hitting "Menu" once again. From the list of options, choose "Import contacts from SIM" and then press "OK." Note that these steps may vary depending on your phone model, so refer to your user manual as necessary.
Allow the device to copy all of your contacts to its internal memory fully, without interruption. Answering calls or sending messages during this process could halt it, requiring you to restart the process all over again.
Place the new SIM card into the phone and use the "Copy all to SIM" function to move them. This is generally done by pressing "Menu," "Phonebook," and then highlighting a contact and hitting "Menu" again. Choose "Copy all to SIM" and wait for the phone to export all of your contacts to the new SIM card. If you do not have the option to copy all of your contacts at once, a manual process will be needed.
Copy each contact over one-by-one if "Copy all to SIM" is not available. Unfortunately, not all models have the option to copy all of your contacts at once. Instead, you may have to duplicate every contact in your phonebook one at a time. To do this, press "Menu" from the home screen, then select "Phonebook" and highlight the first contact you wish to copy. Press "Menu" again and choose "Copy to SIM."
Repeat the one-by-one copy method for each contact stored in your phone's memory. This process can take a very long time to complete compared to using a SIM copier, but if a copier is unavailable, this is the next best option.
When switching sim cards back and forth, it can get very confusing as to which white chip is the old and which is the new. Use a Sharpee marker to colour in a small "O" on the old card and a small "N" on the new to help you keep them straight.
You must copy the contacts from the old SIM card onto the phone before the chip is deactivated in favour of activating the new one. Some phones may allow you to copy the contacts even if the chip is no longer active but most will not boot past the loading screen without an active SIM card inserted.