A subscriber identity module card is a removable input device in GSM mobile phones. Its main job is to store the service-subscriber key to identify a user on a mobile network. For example, if you have T-Mobile as your service provider, your SIM card is what tells the T-Mobile network that your phone is being used by your account. A SIM card's secondary function is to store information like contacts. This can be useful if you are switching phones because you can bring your contacts with you.
Boot up your Windows Mobile phone and press the start button. Click "Contacts."
Navigate to the contact file that you want to send to your SIM card. Highlight the contact file.
Press the menu key and then click "Save to SIM." That contact file should now be on your SIM card.