The 3G coverage maps in Verizon's ads may or may not have been secretly meant to mislead viewers, but in any case they are technically accurate as labelled. Therefore, any confusion is the fault of the inattentive (or illiterate) viewer. AT&T may have an "emotional" complaint here, but I just don't think they really have much of a "legal" complaint. The courts can't legislate people's attentiveness! (Nor should they.)
Not exactly. An advertising claim can be literally true but still likely to mislead or confuse consumers, a doctrine recognized by the courts as "false by necessary implication." Such a claim is actionable. It is difficult to prove such claims without consumer survey data, but a court will sometimes substitute its own judgment for the consumer (although this more often happens in disputes before self-regulatory organizations such as NAD).
Also, the courts don't legislate. That's the legislature.