Wi-Fi may be plentiful these days, but it's far from ubiquitous. A device like the iPad is just begging for always-on Internet access, whether it be for checking mail, surfing the Web, or even keeping up with your latest game of Words with Friends HD. Apple's iPad Wi-Fi + 3G delivers on that promise, though the 3G experience may occasionally have you searching about for a Wi-Fi access point tout de suite.

Everything we said in the original iPad review holds true with this device, as the differences between the two models are few. Outwardly, the 3G-enabled iPad is almost identical to the Wi-Fi model, and the two share almost all of the same features, with the exception of those related to 3G networking and GPS.

iPad 3G

For the privilege of those few features, however, you will be paying a bit extra: the 3G models command a $130 premium over their Wi-Fi-only siblings, making the price tags $629 for the 16GB version, $729 for 32GB, and $829 for 64GB. And keep in mind that the higher price covers only the 3G hardware inside the iPad. In order to actually use the 3G service, you'll need to pay for one of the two monthly that Apple and AT&T have teamed up to offer: a $15-per-month plan that allows you 250MB of data transfer or a $30-per-month plan that allows you unlimited data. And unlike the iPhone service agreement, which requires a two-year commitment with AT&T, you can cancel your 3G plan for the iPhone at any time.

The performance

If you've spent any time with an iPhone 3GS, then you'll be pretty familiar with the iPad's 3G performance, as under-the-hood investigations show that the two use the same hardware.

Given that the iPad also boasts the latest 802.11n Wi-Fi specification, there's no contest between the two: Wi-Fi will beat 3G every single time. I ran a few speed tests using the Speed Test iPhone application and, though unscientific, Wi-Fi's superiority was readily apparent. At my home, Wi-Fi was an astounding 70 times faster at downloads and 30 times faster at uploads.

iPad 3G vs WiFi

Of course, such performance varies widely depending on the quality of the network in your location. And given that poor performance on AT&T's 3G network has been one of the major complaints with the iPhone, don't expect magically better performance on the iPad. The apartment to which I recently moved resides in a spotty coverage zone for AT&T's network, and I've experienced frequent signal drops, poor coverage, and slow service on both my iPhone 3GS and my 3G-enabled iPad. I also have one of Apple's recent 802.11n AirPort Extreme Base Stations, which helps me get the most out of my Wi-Fi network.

If you live, work, or otherwise spend a lot of time in a place with solid 3G coverage, you should find the iPad's 3G performance to be perfectly serviceable for most common tasks, like reading email, surfing the web, checking RSS feeds and keeping up with social networking sites like Facebook or Twitter.

But when you start to get into more intensive tasks, the cracks in the 3G network begin to show. While I was able to stream video, audio, view maps, and so on over the 3G connection, the performance was sometimes subpar. Streaming via Netflix's iPad app, for example, yielded video that was mostly watchable, though it did suffer from frequent pauses in playback as the video re-buffered.

The quality of the video delivered over the 3G network is also noticeably lower than what you get via Wi-Fi. Netflix, for example, down-samples the video, though it's passable. I also tried the AirVideo video streaming app, which allows you to pick and choose from a variety of data rates, but I still had trouble with pauses in playback.

I had even worse luck with the recent ABC Player update, which allows for streaming video over the 3G connection. Performance varied hugely depending on location, with streaming basically impossible to use at my home. However, I did find that other locations yielded better results, and in one particular incident, I actually had to flip the iPad's cellular data connection off and then on again to yield better speeds.

Most perplexingly, I found that YouTube videos streamed over 3G were practically unwatchable, due to their low quality. You appear to get the same videos that the iPhone gets over the 3G connection, which look terribly pixelated on the iPad's higher resolution screen.

In general, pretty much any bandwidth intensive task from video streaming to rendering graphics heavy web pages takes longer to complete via the 3G connection, but when you're out and about with nothing to compare it to, it's not much of a bother.