Moving to Korea

Hey, I am planning to move to Korea next year or so .. after I finish my bachelor degree here. I haven't been to Korea since I was 9 years old, but I do speak Korean pretty fluently but my writing sucks. I plan to work for government in Korea and according to the Korean government, I first need to change my citizenship back to Korean and serve military... Anyways, I want to get ready to move back to Korea and I need help with few things.

1. I was wondering If I can legally change my name to English name, because past 14yrs of my life, that's what I have been called and people know me as.

2. Where is best place for english speaker to settle down? If not, I was planning to live at relative place in bundang (i dont know if that is correct).

3. What kind cellphone services do Korea offer? Should I just take my phone from here?

I'll think of more as time comes... thanks