If you have someone in Oklahoma you're trying to get in touch with, the Red Cross is recommending you try to text rather than call. You can also check the "Safe and Well" website to see if your family and friends have checked in.
This is also a good time to remind you about the Red Cross's Tornado App for smart phones. It has a built in tornado siren that activates when your area is in danger.
It also has a complete list of shelter locations.
Plus, the app includes the "I'm Safe" button to send alerts to your friends and family through social media.