@mariak24: The reason is unknown. but use the process of elimination & you'll be able to narrow the causes of the
Unregistered SIM-card. PS try this tricks, while you get more answers.
1) Take off the Phone cover, remove battery & check SIM-card, could be loose or dirty, re-install it & ensure SIM is tight.
2) Install a SIM-card, from a compatible device (iPhone, Samsung,.etc.) If it works Phone is Ok (Test Ur -SIM in another Phone too.
3) Contact -Telus Online & Chat with an agent or dial *611..Could be that, service is disabled by technical error.. PS report results to forum,. <ReadMe-soon> "v9"