I have received a letter at work that I have to reply to from a Korean. My problem is that I don’t know which is his first and which is his last name. The name is given as: Choi, Sun-Im (PhD).
Can anyone help me? I don’t want to cause an international incident of epic proportions. 
The family name is Choi.
It’s Dr. Choi.
Thanks!
In Korea (as well as a few other countries), the family name is given first followed by the personal name. Some people, as the academic mentioned in the OP, when writing in English place a comma after their family name, some people just transliterate their name as they would give it in their native language, and some people give their personal names first followed by their family name.
The Vietnamese have an interesting twist on that: In Vietnamese, the family name comes first followed by the middle name (quite often merely ‘male’ or ‘female’ {depending on the gender of the person, of course}) and finally the personal name. When giving their name in English, the middle name remains in the middle; just the family and personal names switch positions.
Nitpick: No, that’s not your problem. Your problem is that you don’t know which is the surname or family name, and which is the given name(s).
For example, take a typical Japanese name like Yoko Ono. She has that name order in an English-speaking environment, but in a Japanese context she would be “Ono Yoko” – so the first and last name switch around, but her surname is still Ono and her given name is still Yoko.
For further complication, a lot of people do not have a surname or family name, but that’s another issue altogether.
And its definately Dr. Choi. Don’t use his given name. And definately use the honorific.
I forgot to mention something about the name in the OP. Although it’s spelled in English (and even in Korean: 최) Choi, it’s pronounced to rhyme with weigh.
Well, that didn’t work out quite right. Take 2 with the smilies disabled this time!
A lot of Vietnamese have Van as their middle name, so does Van mean “male”?
So why wasn’t it transliterated “Chey” then? Do you know why they decided to spell it “Choi” instead?
It’s one of several middle names which are used for men. As this page states:
Well, it used to be pronounced–quite a long time ago–as though it rhymed with toy. It’s still spelled that way and the transliteration is really just a transfer of the Korean spelling to the English spelling.
Nitpick: For a typical Japanese name you’d be correct, but not in this case. Yoko Ono’s name is Yoko Ono.
The katakana above reads “Yoko Ono.”
A better example would be the Japanese PM. We call him Junichiro Koizumi, they call him Koizumi Junichiro.
I wonder if that’s a not-so-subtle way of indicating that she isn’t “one of us” anymore. I mean, she is kind of considered to be a fruitcake by a lot of people.
The answer is obviously a “yes”. The question is whether this sentiment comes from her or the Japanese, and I think the answer is that it’s more or less mutual. I understand Alberto Fujimori is in something of a similar situation.