One of the phone's best features is its high-speed LTE connection, the first on a Windows Phone. I found the connection to be quite variable, ranging from about 7 Mbps to 13 Mbps when I tested it in Cambridge, Mass. Reviewers in other cities found variable speeds as well, generally ranging from 8 Mbps to 20 Mbps.
Even at 7 Mbps, though, the Lumia 900 is much faster than normal 3G connections available on Windows Phones, and transforms the experience of browsing the Web, downloading, and using data-centric mobile apps. Normally when I do that on a Windows Phone, I know I'm on a phone because of slow downloads and delays. With LTE, heavy data usage feels more like it does on a broadband-connected computer. If you've got a need for speed, and you want a Windows Phone, you'd do well to consider the Lumia 900.
And it's inexpensive: A 4G phone that can be had for $99 isn't currently easy to find. But soon 4G will be commonplace on $100 phones, including two upcoming Android-based phones: the LG Viper 4G LTE on Sprint and the LG Lucid on Verizon.
Also keep in mind that AT&T's LTE service isn't available everywhere -- at the time of this review, it was available in 31 cities in the U.S. And speed comes at the expense of battery life. When using LTE heavily for browsing the Web, downloading and using data-intensive apps, I was unable to get a full day's use out of the Lumia 900. In moderate use, it lasted the day. (The 1830mAh battery, unfortunately, isn't replaceable.)
The phone runs Mango, the latest version of Windows Phone software, but AT&T and Nokia have stuffed some extras in as well -- and these extras are a mixed bag. Nokia's App Highlights app is nearly useless; it merely highlights apps that you can find in the Windows Marketplace. On the other hand, I appreciated the AT&T Navigator GPS app and the AT&T bar code scanner. Overall, though, I wasn't impressed by the additional software that ships with on the phone.
Windows Phone itself, though, truly shines on the Lumia 900. The LTE connection means that data piped into the operating system's live tiles, which display constantly changing data such as social networking updates, pops in quickly. The large screen with rich colors and crisp text shows off those colorful tiles to their best effect.