The business doctorate:

Should I get a Ph.D in Business or an MBA?

It is generally agreed that the business masters degree is more appropriate for those who intend to apply their learning in the "real world," while the doctorate is geared toward those pursuing an academic career.

Normally, the prospective student has a wealth of undergraduate training in mathematics or a similar quantitative area; however, some are allowed to "make up" prerequisites, which adds to the length of the program. 

The doctorate in management typically takes four to six years to complete and consists of 2 years of course work, the qualifying exam, and a dissertation.

One really must consider the opportunity cost of such an undertaking.  While virtually all doctoral students receive some financial assistance from the university, it is not what one might consider high salary.

Elite international students. 

If you are the cream of the crop, this may be one way to become a U.S. citizen.  Many of the business phds I know are from other countries.  

If you thought getting into top MBA was hard...

The required GMAT score for consideration at top institutions for the PhD approaches 800.  You definitely need some GMAT coaching!