Well, that came out of nowhere. Although we knew the device existed early this year, today’s arrival of the Dell Aero at AT&T Mobility was a total surprise – at least to us.

And also a bit of a mystery. 

Dell’s Aero smartphone runs not Android 2.2, 2.1 or even 2.0.  The Aero runs Android 1.5 which is so, well… HTC Hero.  Even the Dell Streak tablet runs Android 1.6.  Dell doesn’t think a year-old OS is a problem though, noting that the Aero is running  many “Dell user interface enhancements.”  One would hope.

Features include a 3.5-inch capacitive touchscreen (640×360), UMTS/HSDPA mobile broadband, 802.11b/g Wi-Fi, Bluetooth 2.0, a 624Mhz CPU, a microSDHC card slot (a 2GB card is included, 32GB max), GPS, a 1000mAh Li-Ion battery, and a 5MP camera.

Leaving the disappointing OS version aside, the Aero has a few selling points.  First, it’s only $99 with a two-year agreement, a price which is certain to drop in the coming weeks, at least from third-party retailers.  It’s also a great looking device that’s thin and sleek.  And at only 3.6-ounces, it’s quite light-weight for an Android-powered phone.

You can order the Aero today via Dell.  The handset is slated for direct sale by AT&T “soon.”