With the introduction of 3G, and especially 4G, mobile Internet access is no longer considered inferior to home broadband. In fact, in certain locations, it can actually be much faster than many residential DSL plans.
That said, as you roam around, even within one city like the case of the iPhone 4S, you'll experience changes in connection speed and coverage. That's just the nature of any cellular data connection.
Generally, it's best to use a 4G connection. However, since, for now, none of the wireless providers can guarantee the availability of 4G coverage throughout the U.S., it's better to have a device that also supports 3G, which is slower but with much more ubiquitous coverage.
Some smartphones, such as the iPhone or certain Android-based handsets, can work as a temporary mobile hot-spot solution to share its cellular connection with other Wi-Fi devices. However if you want to have a more permanent connection, I'd recommend a separate solution. After all, you'll also need the phone for its intended purposes, such as talking.
Following is a list of mobile cellular Internet solutions that are worth considering for those who travel frequently. They include mobile hot-spot routers that support multiple Wi-Fi clients (usual five clients) and cellular USB modems that work with just a single computer.
Mobile hot-spot routers
T-Mobile Sonic 4G Mobile HotSpot
This is the latest among mobile routers; the device supports both 4G and 3G network in an excellent compact design. It's the first from T-Mobile that supports theoretical data speeds up to 42Mbps for download. In real-world testing around San Francisco, however, it offered far lower download speeds, at around 3Mbps, which is still fast enough for most Internet applications. Read the full review.
Clear Spot 4G Apollo
The Clear Spot 4G Apollo is an excellent mobile router with very good battery life and a helpful/practical design. While it's not compact enough to tuck away in your wallet, it comes with affordable and, most importantly, unlimited data plans. The catch: it supports 4G only, meaning when out of Clear's 4G coverage area, it's useless. That said, it's the best mobile solution for those who travel or live within the provider's 4G coverage area. Read the full review.
Sprint MiFi 4082 3G/4G Mobile Hotspot
This tiny device offers an amazing set of features, including network storage, modem tethering, and GPS-based local service finder. The router offers decent connection speed and has about 4 hours of battery life, which is not bad but shorter than what the other two offer. Read the full review.
Verizon's Samsung 4G LTE Mobile Hotspot
Measuring just 3.5 inches by 2.3 inches by half an inch, Verizon's Samsung 4G LTE Mobile Hotspot is one of the most compact and good-looking mobile router on the market. It supports both 3G and 4G networks and offers excellent data speeds in our testing, around 9.5Mbps up and 7.5Mbps down in the San Francisco Bay Area. The catch: it has short battery life and doesn't come with many features, not even a battery gauge, which is crucial for a mobile device of its type. If you don't mind keeping it plugged in once in a while, it still makes an excellent mobile Internet solution. Read the full review.
Mobile cellular USB modems
T-Mobile Rocket 3.0 Laptop Stick
Similar to the Sonic 4G Mobile HotSpot, the Rocket 3.0 Laptop Stick is supposed to offer up to 42Mbps download speed, according to T-Mobile. In our testing, it didn't but it was still very fast. The modem comes included with T-Mobile's Wi-Fi hot-spot service and limited data plans. However, when the monthly caps run out, it still works, just at much slower speeds. The modem comes with built-in software that works with both PC and Mac, which means that all you need to carry is the modem itself, without having to worry about the software CD, in case you want to use it with a different computer. Read the full review.
Verizon's G VL600 LTE USB Modem
This is the single-user mobile access solution of the Samsung 4G LTE Mobile router, which means it's superfast. The modem also offers text messaging. On the downside, it's rather bulky and doesn't include the required connection software within itself; make sure you carry the software CD with you if you want to use it with another computer. The modem also works only with Windows. Read the full review.
A final note: Although these devices are actually small enough to carry in your pocket (or even wallet), despite the headline, it's a better idea to keep them out in then open while they are turned on. For one, all of them generate a certain amount of heat, sometimes hot enough to be dangerous when used in a closed area. And secondly, which is also the most important, they are all cellular devices, which, similar to cell phones, might not be very good for your fertility.