Voice-initiated searches on the Google iPhone app account for about 7% of overall Google search query volume on the iPhone, according to search-based ad network Chitika. By contrast Google CEO Eric Schmidt said previously that 25% of Android-based Google searches in the US market are initiated by voice.
Below is a chart reflecting Chitika's data, based on millions of queries, that show the proportion of voice to non-voice initiated Google queries on the iPhone. While all Google voice search queries come from the Google app, the non-voice queries presumably are distributed across the app, Safari toolbar and Google.com mobile site.
The data in the chart above may not be exactly reflective of all voice search on the Google iPhone app. But let's assume that they are generally correct. That makes the two numbers cited (voice on iPhone vs. Android) very interesting -- and curious. There are other voice search apps on the iPhone (e.g., Bing, Dragon Search, Yahoo) and we don't know what those queries volumes are at the moment or how they compare to the Google breakdown of voice vs. text-based search.
The volume of voice-initiated search queries (25%) on Android is striking by comparison the 7% iPhone number. Google has more deeply integrated voice into the Android platform and may have trained people to use it more frequently accordingly. I can't explain the discrepancy otherwise.