I am having this problem too. I recently bought the Frontier S3 and have used the voice input a few times and it worked just fine on v2.4. However, I upgraded to 3.0 last night and tried the voice input this morning and it doesn't work at all. I keep getting an error message saying "Voice input unavailable". Very frustrating! After researching this, I am surprised at how long this problem has been going on! Has anyone found a fix for this?
SVoice has been marginal since it first came out. Samsung just isn't improving it and we're expected to live with it. They'd be wiser to accommodate OK Google. At least that works!
I reset my S3 (Settings->Device->Reset Gear) and voice input is working again. Since my watch only a few days old, I did not do a back up and restore. So, when I set it up after the reset, it was all from scratch. I'm glad voice input is working again. Hopefully it will stay that way!