As an enthusiastic iPhone user I want to attribute this growth to Apple but suspect it's mainly:
- mobile phone operators offering reasonably-priced (?) flat rate deals with unlimited internet access;
- said mobile phone operators advertising the benefits of being able to access favourite sites ;
- the proliferation of handsets and mobile browsers that give users access to a web that looks recognisably web-like (and not a horribly adulterated version). I think the iPhone set a standard that others still have to beat - there's no 'iPhone 'killer' yet although Samsung and LG are gaining ground - unlike Nokia and Blackberry.
Related to this I guess is the growth of the 'mobile app'. Here Apple's influence is again dominant with Microsoft and Nokia opening their own applications store. The apps I use on my iPhone for Facebook and Google are great - I wish we had something like it for our VLE.