If you’re showing ads to cell phone searchers, you can now specify – in some countries – which carriers you want to display your ads. See the image below for your current choices.

Based on regional preferences (i.e. in the US, Verizon very strong in the Northeast, not so hot in the Southeast, as I’ve discovered since moving to North Carolina and having to climb on top of my washing machine to get reception in the house) or other considerations (AT&T has an iPhone exclusive right now), you may want to limit your ads to a particular carrier’s users.