Mobile web browsing is slightly different than the traditional, "desktop" internet. Whereas the desktop web is served via an internet browser, there are many ways of serving mobile websites and advertising. Mobile advertising exists across a number of platforms. Ads can be served on WAP sites, full websites via mobile devices and inside apps. Each requires a slightly different perspective.
Mobile devices use Wireless Application Protocol (WAP) browsers that automatically load a mobile website, sometimes called a WAP site. WAP sites are built to accommodate a variety of devices -- both powerful smartphones as well basic cell phones; those with less computing power. Out of necessity, WAP sites are less graphically heavy than their desktop counterparts. As well, they are built specifically with smaller screens in mind. WAP sites can be identified by the "m." at the start of their URL. However, the newest, most advanced devices can access both the WAP as well as the full desktop website. Compare the home screen of Yahoo.com from a desktop browser with that of m.yahoo.com viewed from the iPhone.
Advertising in apps has further complicated matters. All apps are not created equal. Each is a different experience for the consumer. There are no standard layouts or user interfaces to make it easier for developing ads that run across many premium apps.
Before you commit to a mobile campaign, decide which of these platforms suits your needs.