Here is what I found on google about this subject.
This feature is experimental, which means a couple of things. First, similar to other voice-recognition technologies, the accuracy of voice recognition will improve over time as more people use the voice search feature. Second, the feature is currently only supported on 8110, 8120 and 8130 BlackBerry Pearl models in the US. Third, we'd love to get your feedback on it -- feel free to leave your comments below.