Assistant uses a feature called 'Conditional Call Forwarding' to receive your rejected calls and connect you to our system.
You need to make sure your US Cellular plan includes the call forwarding feature.
I have Call Forwarding
1. Disable your phone's Wi-Fi connection.
2. Open your phone's dialer, dial *90*5595335694, and press the send button.
Note: Press the dismiss button when a notification appears on your phone. If the message states that call forwarding activation was a success then you are done. If it fails then redial the activation code.
3. Go back to the app and try to activate the service.
*Only available in the U.S.