...
If the call fails, first check that the PrivateGSM configurations are correct and if not, fix them and close the Incident. If they are fine, let's escalate to the second level
If PrivateGSM reconnects to perform the test call, then most probably we had a Temporary Network Problem issue. If the test call goes fine, check if the PrivateServer is configured with one or more Outgoing trunks. If almost one trunk is present, then you need to escalate.
On the other hand, if no trunks are configured, let's check if the User can call other party now, if he (she) can then close the incident.
If the User still can't call then check that the other device is connected and registered and if it doesn't, close the incident as "Not an issue". If the other party is connected and registered then escalate to the second level.
...
Second Level
We can receive an escalation request for three reasons: a User's remote party configuration needs to be checked, we have to check wether one or more trunk are configured, a general network status check.
...