An inactive USIM, or Universal Subscriber Identity Module, error can cause a lot of problems. On top of not being able to use the phone to make and receive calls, messages or to view web pages, it means that users cannot access their contacts or any other important information that is stored on the card. Thankfully it is very easy to diagnose issues with USIM cards, whether it be an issue with the card itself, or on the carrier's end.
Take off the back cover of the device and remove the battery. Ensure that the SIM card is properly inserted into the phone, facing the right way. If unsure as to how the SIM card should be inserted, look for a visual aid near the SIM card slot, or consult the phone's owner's manual.
Remove the USIM from the back of the phone. Check the USIM for any damage, especially on the metal connectors. If there is any damage, the USIM must be replaced with a new one.
Call the phone provider's customer service number and ask to speak to a representative. Once on with the representative, explain the issue to him, and ask him to verify that the card has been activated. The representative will look into the issue, and attempt to find any issues on his end.
Visit one of the carrier's retail stores. While there, speak to a consultant about replacing the card. The consultant will be able to assist in activating a new USIM and insert it properly into the phone.