You can enable auto redialing to automatically redial a phone number when the intended recipient phone is busy.
Auto Redial Configuration
Auto redial must be enabled in the phone's settings before it can be used. You can also configure the number of auto redial attempts and the time to wait between redial attempts.
To set up auto redialing:
Using Auto Redial
When you dial a number but fail to establish a call, after enabling auto redialing the phone prompts to auto redial the contact. Select OK to activate auto redial.
The screen displays the redial times and interval. The phone will retry as many times as configured until the intended recipient answers the call.