I have been studying the language and attempting to get semi literate but not merely for seeing K-girls.
I do find they like the effort I make and if I can say little things during the session which make the interaction a bit better. Mostly though, I think it helps put many more at ease with their own limited English and when they feel a bit more relaxed with me things just seem to be better. This also seems to work a bit even when the woman actually speaks English better than she lets on -- pretending not to understand is a good defense mechanism and to some extent control mechanism. But many seem to see my efforts to speak some Korean as at least a small form of respect for them as a person -- specifically a Korean person -- so the trust level moves up a little.
Now, if you're planning on learning enough Korean to tell them what you want or how to talk dirty in Korean to them expect to both spend a lot of time on that site (seems like it might be good from a real quick look) and then learn the slang from the K-girls.
If you just want some phrases:
Anyeong or, more formally so perhaps good for the first meet, anyeonghasayo: Hi or Hello You can follow the latter with pan-gap-seum-ni-da (nice to meet you) if you like. Not sure if pan-ga-wo-yo or pan-ga-wo would be the form to use if you want to avoid a rather formal tone.
Jeongmal yeppuda: you're really pretty
bogo shpeotseo: Have wanted to see you -- you might use jeo jeongmal (I really) in front of that if you want to.
jeongmal jalhanda: you're really good at this. (If you have not figured it out jeongmal = really so you can use that on its own like you would in English -- surprise that something is true or expressing some doubt playfully using inflection.)
ppal-ahjweo: is asking for a BJ
woonri haja: lets do it when you're ready to get to the main event.
na ssanda: I'm cumming
jinjja jeoaatseo: it was really good (jinjja is another word that can mean "really")
woori ttohaja: lets do it again
gomaweo: thanks.
No, I did not know these but long ago one of the native Korean speakers provided the list to a bunch of us. Most of these are in an informal form of speech but you're not likely to be seen as acting rude if you try using them.