can't make or receive calls or send text messages
If the apps are missing from your phone:
Settings>Apps>All Apps, then scroll down to whichever apps are missing from your app drawer (eg. Phone/Dialer, Messaging). Click on the missing app(s), then in the app info screen, you should be able to enable it.

If the apps are there but you can't use the carrier service: Power off your phone, remove the SIM card (if possible) and then reinsert it in the correct position. Then power on the phone.