Refactor code to use inbound_numbers if set

app/delivery/send_to_providers.py

@@ -51,7 +51,7 @@ def send_sms_to_provider(notification):
                     to=validate_and_format_phone_number(notification.to, international=notification.international),
                     content=str(template),
                     reference=str(notification.id),
-                    sender=service.sms_sender or current_app.config['FROM_NUMBER']
+                    sender=service.get_inbound_number()
                 )
             except Exception as e:
                 dao_toggle_sms_provider(provider.name)