Are phone calls recorded by individuals who are from the legal department or at higher authority positions without the callers permission?

To answer if, are phones calls recorded- Storing all phone call conversation recordings would be infeasible. Phone companies keep logs to bill you from (from, to, time, duration, etc) and within jurisdiction they can be court ordered to disclose such information (to an extent). With that said it may also be perfectly legal for the restaurant (a participant in the call) to record all calls for training purposes. I know in Australia it is legal if disclosed at the beginning of the call.

Unless the pranks are violent, sexual or repetitive to an extent of harassment, or to an emergency service (police, fire, medical) I really don't think the police or anyone else in that matter will care enough to follow it up- They hopefully have more important things to worry about.

If you are concerned, consult legal advice as recommended by Terry Chia.