How many Window Phone 7 units has Microsoft sold? For whatever reason, it's difficult for Microsoft to give a straight answer. That, of course, leads to industry speculation that things aren't going so well for Microsoft's new mobile platform.Why do people always assume the worst when a company doesn't reveal its numbers? Mainly because when a company has a big success, they're more than happy to open up the spreadsheets and crow about what they've done. Microsoft is no different in this respect, bragging that they sold more than 2.5 million Kinect units for their Xbox line of game controllers in less than 30 days last month.

Microsoft seems to be making the right moves as far as the logistics of this launch. Working Windows Phone 7 demo units are available at carriers (I saw two at the local mall's AT&T store) and Microsoft even has its own Windows Phone 7 kiosk elsewhere in our mall. In the case of AT&T, the phones are competing with iPhone, BlackBerry, and Android devices. The other carriers have everything but the iPhone. With so many established competing devices on all the major carriers, it wouldn't be unsurprising and forgivable if Microsoft had some tough sledding ahead.

The one official data point that we do have is that 1.5 million devices have been "sold to carriers" in the six weeks since the Windows Phone 7 launch. As a point of comparison, Apple said that three million iPhone 4 units were sold in its first three weeks. So on first glance it appears Apple had a run rate of about a million units a week, whereas Microsoft's rate was only about 250,000.

In reality the gap is likely to be larger, because we're not comparing the same kind of numbers. Apple's "sales" are not the same as the "sales to carriers" Microsoft describes. When Apple sells an iPhone to a user from one of their stores, the user has the unit in hand and has paid for it. When Microsoft sells a phone to a carrier, it's simply "in the channel," either in a warehouse or the back room of a carrier's local store. For all we know, many if not most of those phones are still stacked up waiting for a customer to buy them.

It could take several more months of true sales to consumers before those inventories of "sold" Windows Phone 7 units are actually sold. In a catastrophic worst case, the phone inventories might not sell at all if spiffy new models come out and make the current ones obsolete. So who is actually taking that inventory risk? If the phones don't sell, Microsoft may actually have an agreement in place where they have to buy back the phones. You see those kind of contracts for book sales for example; bookstores can pull year-old books off their shelves and return them to the publisher for credit. Given the experience that Verizon had with Kin, it seems unlikely that the carriers didn't think to protect themselves from this possibility.

So, that's the worst that can happen? What is really happening? Microsoft knows, but they're not saying.