As from 21 April 2015 Google will include mobile seo as a ranking factor. Voice search is increasing as the most favored method of finding information on the WWW through especially the Google browser.
On April 21st Google are enforcing their new 'mobile friendly' alogorithm, you can read about it here: http://googlewebmastercentral.blogspot.com/2015/02/finding-more-mobile-friendly-search.html