Political pollsters have been under pressure to make sure their samples include Americans who rely solely on cell phones—and the latest NBC News/Marist polls of Florida, Ohio and Virginia exhibit why.

As NBC's First Read flags, Romney narrowly pulls ahead in Florida among voters who were polled over landlines—48 percent to 45 percent. But among cell phone respondents only, Obama has a major lead: 57 percent to 34 percent.

In Virginia, the results are similar: Romney leads by 1 point among voters polled over landlines: 47 percent to 46 percent. Meanwhile, Obama has the advantage with cell phone respondents: 54 percent to 36 percent.

In Ohio, Obama does better among both landline respondents--44 percent to Romney's 41 percent--and cell phone users--47 percent to Romney's 37 percent.

According to the poll, 28 percent of its respondents in Ohio and Florida were cell phone users, compared to 27 percent in Virginia.

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