Embarking on a mobile ad buy is diving into a dark, deep sea crammed full of startups you've likely never heard of: Celtra, Mojiva, Medialets, inMobi, just to name a few. It's brimming with a lot of little companies -- and a couple of big stakeholders like Apple and Google -- scrambling to build the infrastructure to make advertising work in a medium that some have said will be bigger than TV.
