I never see any ads on my BlackBerry; dunno why but I suspect there must be some kind of blocker built in. They show up on my iPad and iPod Touch just fine.
I suspect it's just an issue with your phones, and not necessarily your ads. You could try a different browser (like installing Opera) and see if they show up there.
Mobile advertising is still something of a conundrum. The various methods I have for serving it can't seem to keep up with all the User Agents and there is definitely not a universal experience, even amongst smart phones. I think we're just kind of in a tweener period before it all settles out.
Yea, I think we're still kind of flying with one eye closed in mobile. Last year I made a sizable amount on one of my sites, but I never once could see the ads myself - I had to just trust by the income that they were running, and to this day I have no idea how many mobile users actually really and truly saw them.