If the person at the front desk is not normally engaged in customer service or guest service, and he does not have a rapport with a preferred cab company, then it probably behooves him not to call cabs for visitors.

For there is the chance that the visitor might have gone to the rest room or have changed his mind and is now a no-show for the taxi whose driver comes into the lobby asking who called the cab company.

In this day and age (the cell phone era) most people don't need to ask where a phone is let alone ask someone to make a call. Therefore asking the security guard to call a cab is even more out of line.