Of all the things that my cell phone is missing, I do not count ads among them. In fact, one of the things people feel is most intrusive regarding mobiles are cell companies advertising to you over text. And yet, Microsoft feels that we need even more ads.
As such, Microsoft today is launching mobile-sized banner ads, to be displayed inside web browsers on a PDA. Then again, they aren't alone - Yahoo and Google are both pushing ads into mobiles as well. You can't blame them. Search, after all, is funded almost exclusively by advertisement.
As display quality on mobiles improve, it might not be so cumbersome. However, speed might still be an issue. Hopefully, any ad technology they deploy will be smart enough to not bog down a phone during loading. I have a feeling, however, that it will not help.