Is it possible to send a text message from a New Zealand Vodafone Cellphone to a Korean Cellphone?

I have tried txting my friend in Korea with no luck although he was able to ring me on my cellphone from Korea.

Does Vodafone suport texting to Asain countries because at the end of last year, I tried texting two of my friends in China and they couldn't get any of my text's but when I went to the USA for a couple of months, I was able to send them text's and they were able to send me texts as well.

I have tried every combination I can think of to input the numbers for texting to China and Korea but so far, the only way is to send them a text from Skype and then they reply to me using skype...so basically we can't communicate unless we ring, or unless we are by a computer (in which case, just use MSN)

Any info will be much appreciated.