Microsoft has partnered with Ingenio to bring sponsored search results to Windows Live mobile search.

Ingenio's entire pay-per-call ad inventory will be available for geo-targeted searches, with only one relevant placement appearing per search, Greg Sterling writes on the Search Engine Watch blog. If no relevant placement is available, then no sponsored link will be shown. The deal is significant for Ingenio and might signal a broader relationship in the future with Microsoft, Sterling writes.

All three of the major search players now offer mobile search sponsored listings. Mobile search advertising is still a small market, but solid growth is expected.

Response rates for mobile search ads are generally much higher than those of online searches, with the needs of the user usually more immediate. Those high rates should lead to more competition and growth.