8.3.8. First Call after Device is Turned On Takes Several Seconds to Ring, Sometimes Goes
Directly
to Desk Phone 
After turning on the Android device, the first call takes a long time to ring or goes directly to the desk phone. This happens because the Android device is still finishing its startup.
When the device starts up, it has to reload all apps that are configured to be permanently
running (OpenScape Mobile Pro is one of them). While it is doing that, the device
is spending most of its time loading and initializing the apps, leaving not much time
for the apps to do their work. It takes one to two minutes to finish the initialization.
After that all apps, including OpenScape Mobile Pro, should be responsive.
‣ Parent topic: Section 8.3. Troubleshooting Specific Issues