You have to make the initial call to express interest in a position. A Ph.D. candidate's application would rise to the top of the pool. The US Information Agency does not do much outreach, but the State Department is recognizing the need to do so. Entry to Foreign Service is based on written exam offered once a year. Class size is also limited by budget.
Applicants have to be flexible and look around for opportunities.
Usually it takes a year to be hired. There is a plethora of jobs. Having a Ph.D. will make you a top candidate, but there is no active recruitment in his firm. About 15 years ago, there was a decline in resources that was difficult and many people left. The US Information Agency consolidated into the State Department about a year and a half ago.