Microsoft has five official partners that will be building devices running Windows Phone 7. Some are old partners. What may be more telling is who isn't on the list.It is no big shock that Samsung and HTC are partners. They have been with Microsoft for quite some time on the Windows Mobile platform. Samsung in particular has been quite visible with its WP7 phone that has been making the rounds as a developer or review device. Even though that particular model won't ever see the light of day in the retail market, Samsung will definitely have a follow-up device or two that will come launch day.

HTC has been Microsoft's biggest partner in terms of the sheer variety of devices they build. LG is a recent partner that got started in the Windows Mobile 6.x days and they are continuing to build devices.

Dell has been a big supporter of Windows Mobile since the Axim days that started with Pocket PC 2002. That continued through WinMo 5, but ended there as devices moved to phones and away from traditional PDAs. Now they are back.

That makes four partners. Now it has been revealed by the Windows Phone Blog that Asus will be joining the party.

Long time partner HP though isn't on the WP7 party list, and that is to be expected. After acquiring Palm, HP's Todd Bradley made it clear that WebOS will be powering all HP smartphones going forward.

Update: According to TechWorld, Microsoft has not formally confirmed the list of five partners, so while it is likely this list is accurate, it is subject to change. I wonder if Microsoft may have a sixth partner in the wings yet to be announced, or could there be one of the five that is on shaky ground and hasn't committed to a Windows Phone 7 product this fall?

Click to see "Slideshow: Microsoft's Windows Phone 7 Revealed."