D-Day (that is, device day) for Nokia and Microsoft has kicked off with their press conference in New York. But speaking to analysts in Helsinki beforehand, Nokia revealed a sales number: it said that it sold 7 million devices so far in its Windows Phone Lumia line. The number is not huge, but it points to a global reach: those sales were across 54 markets and 130 operators.But the challenge in the U.S. in particular is acute. It sold only 600,000 handsets there in Q2.