The T-Mobile SIM Kit from Walmart has a barcode on the back that must be scanned in order for the kit to read as "active" with T-Mobile. If it is not scanned, you cannot activate that SIM card. When you order online, don't expect it to be scanned correctly. My advice is have it delivered for pickup from a store, because they know the details of the barcode. I got mine shipped to my house, and had to go back into a Walmart store in order to fix it (T-Mobile recommended going to a T-Mobile Store, but Walmart was closer for me). What we did in the end was I "returned" the kit and "purchased" it right back, only this time the associate scanned the activation barcode properly. Since it was marked as a purchase, the SIM became active and I had no more trouble. The catch is that the activation barcode must be scanned in place of the UPC barcode upon checkout. So if you face this issue, don't call anyone -- Walmart and T-Mobile will both blame the other. Just use this method and you can activate your service online easily with no problems.