One of the things that you might have missed if you weren’t paying really close attention to the live blogs of the Apple WWDC keynote is that when iOS 7 comes out Siri will be able to directly search Twitter, Wikipedia — and Bing. From a search perspective that’s potentially huge news.

I’m speculating that you’ll still be able to ask Siri to “search the web” and it will use whatever search engine you’ve chosen for Safari (still Google unless changed by the user). However Siri is now much more a legitimate “search engine” with Bing as the index.

Integration of web search more directly into Siri was a missing piece and the thing that made it weaker than what Google has recently put together with Google Now and “conversational search.”

In a way the new Siri-Bing relationship is very much like Yahoo-Bing. Yahoo is the UI on top of the Bing index. Now Siri is the UI for Bing results on the iPhone.

Of course Siri pulls “answers” and content from numerous other sources. How those other sources will interact with Bing results, if at all, remains to be seen. What happens if I ask for movies, sports scores, weather or restaurants? These are all categories where Bing has content but there are existing third party data providers for Siri.

I’m also making the assumption that in iOS 7 if users ask a question without literally saying “search the web” the resulting answer or information will be provided by Microsoft. One could thus argue that Bing now becomes the “default search engine” on the iPhone (more like the default “Siri engine”).

Saying “default search engine” isn’t entirely accurate however. That’s because most people don’t use Siri to search the internet today. Most people use Google either through the browser or the Google app. But as Siri’s capabilities and utility expand it may see increasing volumes of search queries. This partnership could be instrumental in that change.

Here’s how Microsoft describes how it will work:

Starting this fall with iOS 7, Bing will power Siri’s new integrated web search. When users ask Siri a question either the specific answer or web search links will now be delivered automatically so users can find information even faster. Bing was designed from the outset to be a great place for web search helping customers quickly find what they are looking for and get more out of search. We are thrilled that all the great results people have come to know and love on Bing.com will now be available to Siri users on iPhone, iPad and iPod touch.

We won’t know until we can get our hands on it what the Bing integration into Siri truly looks like. But it could be quite significant for both parties. If it’s a well-done integration it could also start driving lots of search volume for Bing. In order for that to happen, however, Apple and/or Microsoft will have to educate users about the capability.

We’ll wait and see what the actual user-experience is like (recall the promise vs. initial reality of Apple Maps) but this could be a very big deal for search on the iPhone.

Postscript: Danny speculates (perhaps correctly) that this deal may well be a prelude to replacing Google on Safari as the default search engine. However the consumer preference is still strongly for Google, which may prevent that from happening any time soon.