The Man from Nowhere : Who was the bad guy speaking English to?

At the beginning of the movie when the bad guys go to the pawnshop, the kick Butt bad guy is speaking English to someone on the cell phone. To be clear since there were a lot of bad guys, this was the main bad guy the good guy fought hand to hand in the end. I watched this with subtitles but he spoke English on the cell phone in that one scene. Subtitles in Korean popped up on the screen when he was speaking English. So who was he talking to in English? No one else in the gang spoke English.

Also, I can't believe the main actor - Bin Won - is the same guy from Mother. That dude got seriously ripped for this movie.

You were incorrect when you stated "no one else in the gang spoke english". First, one of the brothers responds to the dialogue you referenced in English himself (with Korean subtitles to boot). Second, I have no idea how many characters in this movie could speak English and neither do you. We just know that when he spoke in English, he was understood by at least one character he was speaking to.

I'm not sure. One of the last guys that he fought was said to be from Viet Nam. So, maybe the common language between them was english.

Changing the subject, what was the deal with the guy that was a sort of korean Michael Jackson?

The Vietnamese assassin spoke English as well. They have an English dialogue transaction when he says:
"He didn't flinch."
"What?"
"He didn't flinch when I shot the gun."
"SO WHAT?!"