Advertising on mobile phones is perhaps one of the most complicated, least understood potential marketing platforms, at least in the United States. One of the factors contributing to its complexity is the number of players involved in deploying ads on mobile phones. Unlike web advertising, which operates on the principles of an open network (at least for now), mobile advertising is constrained by the carriers, who essentially hold the "keys to the kingdom." For the most part, the carriers own access to consumers, as well their demographic information. The dream of geo-relevant, targeted advertising on mobile platforms can only be unlocked by carriers agreeing to share that information, which is highly unlikely in the short-term given the privacy issues involved. However, despite some of these barriers there is strong incentive for carriers to offset content development and data delivery costs through advertising. Sprint, through its partnership with Enpocket, is the first carrier to offer on-deck advertising on its network.

Another factor contributing to the complexity relates to the creative demands presented by mobile advertising. Advertising on WAP requires maintaining a WAP presence that consumers can click to. As a result, the best opportunity for mobile advertising is to reinforce mobile goals (such as building traffic to a WAP site) and use mobile messages to complement other marketing channels. Targeting is primarily contextual, although the networks also offer daypart, device and carrier targeting and frequency caps.

Mobile advertising also faces the same challenges as the other categories mentioned: namely, reach and scale. To address these challenges, there are now numerous mobile networks that have sprung up to ease the complexity and offer advertisers the ability to deploy mobile ads across multiple devices, platforms and sites. Additionally, many of the traditional web ad networks and publishers are building their mobile offerings as the marketplace accelerates. The challenge for these networks is not related to pricing. Rather, the networks must prove the value proposition of mobile advertising.

Examples include:
24/7 Real Media
AdMob, Inc.
Enpocket
Google AdWords Mobile
Greystripe  (mobile games)
Kiptronic
Medio Systems
Millennial Media
Mobileplay
MoPhap
Third Screen Media  (owned by AOL)
Yahoo Mobile Ad Network