If you are looking for a 3G phone running Android on AT&T, the pickings are slim. (Mostly because AT&T’s 3G bands are not compatible with many other carriers, and most Android GSM phones work with T-Mobile’s 3G bands. If you are willing to drop down to quad-band EDGE data most GSM Android phones will “work” with AT&T, they just suffer from slow networking.)

The first AT&T official phone was the Motorola Backflip. AT&T will sell it to you for $199 with a $99 mail-in-maybe-you’ll-get-refunded-sometime-next-year-rebate if you sign up for a 2 year contract. Perhaps a better bet is to buy it from Amazon without a contract for $339. Or with a contract for 1 cent.
The Backflip has a slower processor than the Nexus One (below), but it does have a fold around full QWERTY keyboard and nifty back-of-the-screen touch-pad so you don’t get grimy fingerprints on your nice 3.1 inch 320×480 pixel screen. Of course, mobile carriers are always slow to upgrade your Phone’s OS, so the Backflip is running Android version 1.5 now, upgradeable to 2.1 at some point in the future…
Also note that if you buy one flashed for AT&T, it is likely to have some features (such as the ability to load applications from anywhere) disabled. You can read my full review of the Motorola Backflip here.

The new phone on the AT&T block is the HTC Aria. This phone is smaller than the Backflip (and has no physical keyboard) with a faster processor, but otherwise the hardware specifications are almost identical. AT&T will charge you $129 with a rebate, but you can get it with a contract from Amazon for 1 cent! Or, you can purchase it without a contract for $339.

If you are willing to pay for the phone, you used to be able to buy an unlocked Nexus One from Google with the correct 3G radio for the high high price of $529. (Don’t forget to click the “AT&T” radio-button!). However, they have sold out of their final Nexus One, so if you want one you’ll have to hit E-Bay!

The Nexus one lacks a QWERTY keyboard, but with a 3.7 inch screen sporting 480×800 pixels, the on-screen keyboard can have more pixels dedicated to it than the Backflip’s entire screen. Did I mention it runs a 1Ghz Snapdragon processor? Your applications will run smooth and fast for 5 hours before the battery dies. Although this phone isn’t sold by AT&T, the software and hardware is officially supported by Google, meaning that upgrades to Android will probably roll out on this phone first. It’s running Android 2.1 right now, and over the air upgrades to 2.2 are on the way!

Now that we’ve gotten the two official and semi-official phones out of the way, lets talk about options for people who don’t mind buying a Windows Mobile phone and installing a custom Android operating system on it! These options are completely 100% not supported by AT&T or HTC (the phone hardware manufacturer), so they are not for the faint of heart. They are also only somewhat stable, do not support all phone hardware features, and in most cases run off of the SD card, so you can expect a serious performance hit.

HTC manufactures three phones for AT&T running Windows Mobile that can run (with varrying degrees of sucess) Android. I will refer to them by their HTC & Android on HTC wiki names: Kaiser, Raphael, and Rhodium. (a.k.a. AT&T Tilt, AT&T Fuse, and AT&T Tilt 2) Before you even think about running Android on these phones, you need to examine the “Port Status” table here, and note what features are NOT supported. Only the Tilt/Kaiser has most features supported, because it’s the oldest phone. The Fuze/Raphael phones are lacking support for the cameras, ambient light sensor, and some bluetooth, and the Tilt2/Rhodium is missing even more. In some cases certain things which you may take for granted (such as speakerphone support) just don’t work.

All three of these phones have a slide out QWERTY keyboard, charge via mini-USB (which is good!) and have proprietary audio jacks (which is bad). The Raphael is probably the easiest to put in your pocket, while the Rhodium has the best screen.

• Kaiser (AT&T Tilt) – Best supported by the Android port, but oldest phone. 400 Mhz processor, 2.8 inch 240 X 320 display, 190 grams
• Raphael (AT&T Fuze) 528 Mhz processor, 2.8 inch 480×640 screen, 165 grams Forum based install instructions and Youtube Demo Video.
• Rhodium (AT&T Tilt 2) 528 Mhz processor, 3.8 inches 480×800 screen, proprietary audio jack, 178 grams