You can block hosts on rooted phone easily, so if it's an ad network, it can be done. If it's first party, or in-content, ala tumblr, it's not been done yet, as

You can block hosts on rooted phone easily, so if it's an ad network, it can be done. If it's first party, or in-content, ala tumblr, it's not been done yet, as far as I'm aware - that doesn't make it impossible though.