Unicom was busy and didn't answer the phone.

1. Check whether the phone is turned on normally. You can't receive incoming calls when the phone is turned off or stopped.

2. Check whether the mobile phone is in the signal coverage area. If there is weak or no signal at the location of the mobile phone, you can't answer the incoming call.

3. Confirm whether the mobile phone has functions such as call forwarding or call barring. Setting these functions will affect the reception of incoming calls.