I have a long standing website (launched in 1996, running advertising since 1999), and I can see the writing on the wall - I need to make my site more mobile friendly. I am planning a responsive design (and have a prototype), but I don't know how to transition the advertising over to that world.

My site currently runs a 728x90 banner at the top, and either a 300x250 or 160x600 banner along the side of the content, all above-the-fold CPM advertising. I use Javascript to serve the tags based on the browser's screen.width property - if the user's browser is more than 1030 pixels wide, they get a Box ad, otherwise they get a Skyscraper.

I am planning a mobile design that will be optimized for a 320 pixel width screen, on the theory that most of my visitors will be using iPhones (supported by my Google Analytics), and the assumption that a 320-pixel width will render in a more readable manner (and more universally) than the iPhone's stated 640-pixel width. My site is mostly numbers and tables rather than text/articles. I have tried the design out on an iPhone, an iPod touch, and a Blackberry, and I am pleased with how it looks.

So my first question is, is that assumption truly the best practice? Are there any pitfalls that I'm not seeing?

Obviously mobile design presents some challenges for advertising; it almost needs to be integrated tighter into the design because otherwise it will not be seen (i.e. a side banner is useless now). The rules for desktop CPM/CPC advertising are pretty simple; put the CPM ads above the fold, don't bury things, and don't put too many ads on the page.

But what is a good strategy for mobile advertising? My ad companies do some mobile stuff, but it is mostly the annoying "hang the ad at the bottom of the iPad screen" type which I want to avoid. The standard IAB desktop sizes don't work for mobile - a 728 pixel banner will cause the screen to zoom out too far; a 300x250 cube will take up the entire page, and the 160x600 will cause too much scrolling. Ideally I'd like to see a mobile ad that is 300 wide by 120 tall. Do such mobile ads exist?

Next, how do people feel about integrating the ads more tightly with the content? For example, if I return a list of search results, interleaving an ad into the middle of the results, ensuring visibility? Or is the better approach to put the ad at the top of the content, similar to the desktop? The problem I see with that is that with a smaller screen size, there just isn't a lot of room for site branding, site navigation, the ad, and the content. The ad would push the content down very far, and I think that the users would prefer to see at least some content as they visit the page - the mobile experience is more geared toward quickly answering a question rather than providing a prolonged browsing experience.

Can someone point me to any resources for mobile design that considers advertising?

Google Analytics reports my site with 45% to 60% mobile visitors these days, and I can't afford to shed that much advertising and make the mobile version ad-free.

Thanks,

Ralph