I have used a Motorola Backflip for a month, and am now trying out an HTC Aria. The Aria is a much smaller phone that lacks a keyboard, but has a newer version of the Android OS (2.1) and has a faster processor. For the rest of my comparisons, keep reading.

Cost
This phone costs more than a Backflip, although you can buy one for a penny on Amazon with a two year contract with AT&T. Or $339 without a plan.

Physical Size
The Aria is a pocket phone. Because it doesn’t have a keyboard, the Aria is considerably thinner than the Backflip, and fits in your pocket well. This is a phone you can carry around in your front jeans pocket (guys anyways). This phone feels like my earlier Motorola Razr v3xx phone when in the pocket, and is quite portable.

Display Screen
The screen is basically the same size and resolution as a Motorola Backflip (320×480 at 3.2in diagonal). Although the resolution is smaller than some larger phones, I’ve found it to be just fine for everything I’ve wanted it to do. At it’s brightest display setting it’s just slightly brighter than a Motorola Backflip, but you would probably never take advantage of this in real situations. Fifty to seventy-five percent brightness is plenty for either phone in normal situations. Android 2.1’s “Auto Brightness” setting works well, and the screen has plenty of dynamic range to support it.

Calling Voice Quality and Speaker-phone
The voice quality from the headset and Bluetooth is perfectly acceptable. I have not yet tested it in a truly noisy environments, but I do not believe it has background noise reduction (I haven’t found a 2nd microphone hole anyways…) The microphone is at the bottom edge of the phone instead of the bottom front, but it’s a small enough phone that this probably doesn’t matter. The “next to your head” sensor is very quick and responsive, and the screen “comes back” as soon as you lift the headset away from your head.
The speaker-phone / speaker works for waiting out hold music, but it is relatively anemic and I wouldn’t want to use it for a conference call. All of my Motorola phones have much better speaker-phone performance.

Cellular Bands / Carrier Lock
It is a “quad band” GSM (or World) phone, so you will be able to get voice and GPRS/EDGE service anywhere in the world. However, for 3G/UMTS/HSDPA/HSUPA, it only supports 1800 and 850Mhz, which means that it will work for AT&T in the US, and a few carriers in Latin America. Because I had purchased the phone used, and not from AT&T, I paid a guy on the internet $9.50 for an unlock code so that I could use the phone with any provider. (The Motorola Backflip unlock code cost $3.)

Speed/Processor
This phone is noticeably faster than the Motorola Backflip. It boots in about half the time, and all the widgets on the home screens appear within only a few tens of seconds after boot-up. When switching between applications or portrait/landscape orientation the switch is much faster than with the Backflip. I do not think you will have any complaints about this phone’s UI speed.

Battery Life
The Aria is running Android 2.1, which has had several battery life improvements built in, and it appears to last longer between charges than my Backflip. However, this is still a smartphone, and you will need to charge it daily. (Once the backflip is updated to Android 2.1 it will probably have a similar battery life.)

Android 2.1 / HTC Sense
Android 2.1 adds some battery life enhancements, and the feature that I really use, WPA encryption support for wifi networks! A few features I like about the HTC Sense UI:

• The dialer automatically searches for contacts as you dial a number. For example, if you dial “546” it will show everybody who has “JIM” in their contact name, or “546” in their numbers. This feature blows Motorola’s MotoBlur dialer out of the water.
• Click home button twice to get an “expose” like preview of all homescreens.

On the other hand, the facebook/twitter account integration wasn’t terribly good. I ended up using the default Android Facebook app, and I just stopped checking twitter altogether. If Facebook/Twitter are your thing, you’ll probably want to use a MotoBlur interface (and get a physical keyboard). The MotoBlur “Happenings” widget is the best I’ve seen for keeping up and interacting with Facebook and twitter.

One annoyance I have is that you can not delay the pattern lock. If you want to use a pattern to lock your phone, it will ALWAYS request the pattern, even if the phone just locked itself after being put down for a few seconds. You can change the screen timeout to 10 minutes, but then you have to push the power button to turn the screen off, which locks the phone! I really want the Motorla Blur / 1.5 feature of being able to have a simple swipe to unlock as standard, and a pattern lock after 20+ minutes of inactivity.

On-Screen keyboard
After using a Backflip for a month, I found the lack of a physical keyboard to be annoying. It definitely reduces the number of Facebook updates/comments and emails that I send using the phone. I have not yet decided if having a keyboard is worth the extra size of the Backflip. Because the Aria runs Android 2.1, it’s on-screen keyboard has a Google speech to text button which works really well for simple messages. I have found it much easier to hit the button, say a sentence (slowly, with pauses between each word) and then send my message back. As long as you are not using weird nouns not in standard dictionaries, and are in a quiet environment, the speech recognition works quite well. I have composed emails a sentence at a time using the speech recognition. The only problem is that it requires network connectivity to Google’s cloud to work. (And every so often when I’m on wifi with perfect 3g signal it claims that the network connection isn’t working!)

The soft-keyboard is acceptable, and has a predictive/corrective text entry system that works well, and is needed due to the mistypes you’ll make. It is fine for typing out a quick message, but people who SMS/email a lot will probably want to buy a phone with a hardware keyboard. Be sure to turn the phone sideways to get the bigger keyboard if you are going to be typing anything longer than a one or two word search term. The biggest thing I miss from the hardware keyboard are the arrow keys to navigate the text selection carrot! It is very, very difficult, even in landscape mode, to click the carrot exactly where you want it to correct a predictive text error.

Button layout and optical joystick
One annoyance with the hardware is the capacitive button layout. The aria has 4 capacitive buttons along the bottom of the screen: Home, Menu, Back, and Search.
Unfortunately, the home button is so close to the left side of the screen that if you hold the phone in your right hand and have slightly longer than average fingers, your little finger will touch this button at the worst time.
The location is also DIRECTLY under the “hide keyboard” soft button on the keyboard, so 20% of the time when you are done typing, you will accidentally go back home instead of returning to the application you were typing in.
In my opinion, putting 4 buttons here made the home and search button get too close to the edges. (I’d be interested in knowing if lefties constantly find themselves triggering the search button.)

From an ordering standpoint, I think having the menu button on the far left would result in less aggravation. (Within an application, pulling up the menu is more easily reversible than going to the “Home” screen.)

On the plus side, the volume rocker (located on the left side of the phone) is easy to use for right handed individuals.

The optical joystick works. I can use it to scroll up/down/left/right within applications that support it. The Frozen Bubble game is the only thing I use it on, because that game doesn’t support using the touchscreen to move the bubble aimer. You “push” the joystick in to select, which is how you take a picture with the camera or start recording with the video camera.
I use the optical trackpad even less than I use the Motorola Backflip’s “BackTrack” control pad. It’s not terribly bad, just not really needed for 99% of the applications. And if an application DID want to make use of it, the constant “clutching” needed of lifting your thumb and moving it before swiping in the direction you wanted to go would get annoying quickly.

The power button is on the top right, which makes us right handed users have to bend our pointer finger to access it. It’s not difficult to push, but I prefer the top left of the phone, where my pointer finger naturally rests.

Music/Audio
Although HTC’s specifications website does not list Ogg Vorbis support, the phone (Android) does support playback of Ogg Vorbis music! I’m not an audiophile, but I found the audio quality to be as good as with any portable music player. The HTC Aria is a small phone, and they have a unique 3.5mm audio jack. Because the back of the phone is slanted, and the 3.5mm audio jack goes into this slanted part of the phone, your headphones don’t quite plug in all the way on the back. (It still works fine.) A picture will illustrate:

Easy to Root!
After waiting and waiting for an easy method of rooting the Motorola Backflip, this phone was a dream to get root access on! The Unrevoked application just handled everything, and everything just worked. Directions can be found here.

That being said, I can only think of one reason to bother rooting the phone, and that would be to make it into a wifi hotspot using the android-wifi-tether software. To make that software work, you do have to download a slightly different wifi driver firmware to your phone’s SD card. Lots of directions can be found here. Everything else I wanted to do with this phone I could do by simply downloading a standard application from the android market.

Battery Compartment / SIM / MicroSD
I bought my phone used, without a manual, and it took me 5 minutes to get up enough confidence to actually yank hard enough to remove the back of the phone. Now that I know what I’m doing, it’s OK, but not super easy. I much prefer the Motorola Backflip’s “push the button and the back panel unlatches”, but I am confident that the back panel of the phone won’t accidentally come lose. You MUST remove the battery to replace the sim card. The micro SD card slot has a nice “push to click, push to release” action, which I find nicer than the “push it in and latch with a plastic tab” on the Motorla Backflip. Oh yes, and the inside back of the phone is surprisingly yellow!

I could not find any external antenna jacks, but most people won’t miss them.

Camera
The camera does not have an LED flash. I can’t hear it actively adjusting the focal length as I do on my Motorla Backflip, but anything farther away than 4 inches is in focus, so this doesn’t appear to be a major issue.
I’ve been able to capture barcodes and other “close up” features without a problem, but it may not work as well for super small barcodes.

It can shoot video up to 640×480 resolution and photos up to 5MP. It offers an option to shoot “wide-screen” format, but the actual CCD sensor is a 4:3 sensors, and you get (2592×1952) in 4:3 format, but only (2592×1728) in 3:2 wide-screen mode. I’m not sure why you would want to shoot in 3:2 wide-screen mode other than to match the screen aspect ratio. It’s not true 16:9, and you are losing resolution. So if you want to use the photos outside of the phone’s display, you may as well leave it at standard 4:3 mode.

The image quality appears to be just as good as the Motorola Backflip when outdoors in good lighting conditions. The lack of an LED hurts in low light conditions. Oh yes, and you actually take a picture by pressing in on the optical joystick. (I had to download a quickstart guide to figure that out…)
Here is a photo taken with the phone’s camera:

Conclusion
Overall, I am happy with the HTC Aria phone. It is smaller and more responsive than the Motorola Backflip, and has slightly better battery life. (It was also easy to gain root access, which allows wifi-tethering.) However, I suspect that the Backflip will make battery life improvements when it upgrades to Android 2.1. Although the Backflip is slower than the Aria, I really only notice it at initial phone boot-up and very occasionally when applications are starting up for the first time. All in all, the Backflip is still quite usable, and the addition of a hardware keyboard really helps with composing emails, text messages, comments and status updates. I will use the Aria for a full month, then switch back to the Backflip to compare again.