I tried Google Voice in the past to send a SMS in Chinese and never successful. I also tried to send SMS to China, failed too. Last week I received a SMS written in Chinese from a China mobile phone, somehow I replied it directly within the Google Voice app and, to my surprise, it went through!
Actually, it failed at the first attempt but then it tried again immediately and show me "Sent":
I then tried several more times, all the same results. I also tested on my computer and verified that my GV account was not charged:
If you are interested, you may give it a try.