SELCAL is a function of the HF radio that allows ground stations to page the aircraft discreetly. Each aircraft has its own SELCAL code and when a ground station calls, you get a tone or two and the SELCAL annunciator. This features provides for the pilots to turn the volume down so they don't have to constantly monitor the racket on HF.

It appears that Mesa's management wants to use SELCAL to call pilots to, i.e. junior man them.....I assume.

Sounds like it's time to write up the HF!

Edit to add; I thought I heard once that some kind of VHF SELCAL exists. Not sure....