SAN FRANCISCO: As smartphones get an increasing array of features, they need faster processors. The Motorola Atrix 4G, billed as “the world’s most powerful smartphone,” arrives with 2 gigahertz of processing power–the kind you’re more likely to find on a laptop than a phone.

That’s notable because there’s an optional laptop dock, which makes the phone function as, well, a laptop.

The Atrix is available now for pre-order from AT&T Inc and will begin selling March 6. It costs $200 with a two-year contract. But if you buy it with the dock, it will cost $500 after rebate, and you’ll have to get a more expensive data plan.

On its own, the Atrix is a speedy phone, though not necessarily eye-catching. With the skinny, light dock, the Atrix is a Web surfing and e-mailing champ, which could make it a good travel buddy. For heavy-duty computing, though, I’d still stick with my full-featured laptop.

The Atrix’s black slab exterior makes it look like other smart phones, but start poking around and the difference is clear: This is a fast handset. With tasks that don’t require a wireless network, such as taking photos or playing games, the Atrix opened menus and applications without hesitation.

The camera seemed to start up faster than those on other smart phones I’ve used, and I could scroll through applications and contacts on its 4-inch screen with ease.

Considering its processing power, I was miffed to see the Atrix is currently running version 2.2 of Google Inc’s Android operating system, Froyo, rather than the newer Gingerbread version, whose faster performance and better on-screen keyboard would match well with the Atrix.

The Atrix works on AT&T’s upgraded 3G network, HSPA+, so to try it out I walked to AT&T Park, where the San Francisco Giants play. There, the phone streamed videos as flawlessly as if I were on my home Wi-Fi network. At my office or home I wouldn’t even attempt to stream content over AT&T’s network as service is unreliable.

Not surprisingly, call quality at AT&T Park was also excellent. My mom, a frequent target of my test calls and sharper critic of sound quality than I am, even said that the Atrix sounded “pretty good for a cell phone.”

But in my office, where AT&T’s reception is spotty, I had to try several times to get a call to go through. When I finally did, a friend sounded muffled on the other end (he said I did, too).

The phone’s display is clear and bright, with good viewing angles that would make it useful for sharing video clips with a friend. When streaming YouTube content, such as Nicki Minaj’s “Moment 4 Life” music video, I didn’t feel as if the colors were as warm as they could have been, though. Like a growing number of phones, the Atrix can play Flash videos — something the iPhone can’t do.

The 5-megapixel camera on the Atrix’s back wasn’t impressive. Photos were crisp, but colors didn’t really pop. And there are only a handful of settings and color effects, so if you want to get creative you’ll need to download a camera app (free ones include Camera 360 Lite and Retro Camera).

You’ll also need to snag an app such as Qik if you want to video chat with a friend: The Atrix has a front-facing camera, but it doesn’t include video chat software.

I expected long battery life, especially with AT&T claiming that you can watch two full-length movies in a row on a single charge. The phone is rated for up to nine hours of talk time, and in a day that included much multitasking and streaming a full-length animated movie from YouTube over Wi-Fi, the battery held up well.

I also expected a lot from the dock, especially because Motorola Mobility Inc. isn’t the first to come up with the idea of combining a phone with a laptop-like dock: One high-profile example came from Palm, now owned by Hewlett-Packard Co, which in 2007 announced and subsequently shelved a laptop-like device called Foleo. It would have acted as a companion to users’ Palm Treo smartphones.

Once I plugged the Atrix into the laptop dock, I entered a combination phone-netbook experience, which gave me more functionality than with the handset alone but not as much as I’d have with a dedicated laptop.

The dock has a bright, crisp screen that measures 11.6 inches diagonally, a full-but-slightly-cramped keyboard and a large touchpad. There are two USB ports and a standard headphone jack. Because the dock has its own battery, it can charge the Atrix while they are attached. Oddly, the dock doesn’t have a front-facing camera, so you can’t use it for video chats.

With the Atrix attached to the dock, a small “mobile view” on the dock’s screen shows you what’s on your phone’s screen — you can use this to access phone functions like making or answering calls or sending text messages, which is neat.

The dock’s main appeal is that it includes the Firefox Web browser, allowing you to surf the Web uninhibited by the limitations imposed by the phone’s smaller display. The dock is great for checking e-mails and visiting websites, and you could use it for some work, too.

Still, it’s not a computer. Without the Atrix plugged in, the dock does nothing. It’s expensive, and you’ll have to add on a $20 per month for AT&T’s mobile hotspot feature (on the plus side, this will enable you to connect four more gadgets to the Internet through your Atrix).

If you’re hankering for a speedy phone, the Atrix is a good bet. I’d hold out on the dock, though. It could be a useful accessory in the future, but for now its price doesn’t match up to its limited functionality.