In Mexico, and in most of Latin America, calling a person you meet for the first time by his or her formal title, such as a Doctor (whether MD or PH.D) “Doctor“, or an Engineer “Ingeniero“, or an Accountant “Contador“, etc., has far greater more social importance than in the United States. 

The title is perhaps an indication of social stratification, separating those who have obtained professional training from those who have not, but whatever the reason for its existence, anyone who does business in Mexico should be aware of the importance of the use of personal titles. 

Jeremy Schwartz provides a nice summary of this social practice in his post here at the Uncovering Mexico Blog.