The New York Times is reporting that Google has added a voice interface to their iPhone search software:

Users of the free application, which Apple is expected to make available as soon as Friday through its iTunes store, can place the phone to their ear and ask virtually any question, like “Where’s the nearest Starbucks?” or “How tall is Mount Everest?” The sound is converted to a digital file and sent to Google’s servers, which try to determine the words spoken and pass them along to the Google search engine.

Other similar services:

• Microsoft's Tellme;
  
• Yahoo’s oneSearch with Voice.