The thing about the Internet is that once you've had always-on access to it at work or at home, then being without it can feel like something of a deprivation. And if you're used to super-fast access, this is precisely what you are going to want while on the move, too.

Modern notebook computers are starting to incorporate SIM slots, so that you can pop a SIM in and use them for Web access over the air. At the moment such laptops are relatively few and far between, and are pretty much the domain of business users. But they support 3G with HDSPA which, where your operator allows, provides for data speeds that can theoretically reach 3.6Mbps.

External modems can provide the same function. In the old days they were built around laptop PC card slots, but T-Mobile has followed Vodafone in launching a USB variant. Actually, the two devices are exactly the same, from the same third-party provider, Huawei.

These USB modems have two great advantages over their PC Card antecedents.

One: they are plug and play, which means you just plug them into a slot, wait a while as their software is loaded automatically and you are ready to go.

Two: obviously enough, they are USB. That means you can use them with any PC that has a USB slot. Designed primarily for laptop users, they'll double up if your main broadband connection, linked to a desktop PC, goes down.

The modem comprises a small, white, plastic lozenge, just 42mm wide, 88mm tall and 15mm thick. It comes in a DVD case along with a pair of USB cables. A short one (20cm) is handy if the USB slot is conveniently located for you to view the modem's connection light comfortably. The longer cable (90cm) is better when the slot is a long way from where you want the modem to sit (maybe on your desktop PC case, for example). It has two ports at the computer end just in case the computer does not provide enough power for the modem through a single connection.

On test, the T-Mobile modem did precisely what was expected of it with no fuss at all. We plugged it into a notebook, waited, and were surfing within minutes. Mac users will have to install drivers manually, though.

As well as allowing Internet access you can manage the SIM card's phonebook and send and receive SMS messages. You can keep an eye on daily, monthly and yearly download and upload amounts, and you'll need to use this to monitor T-Mobile's fair usage policy.

There is little to choose between the T-Mobile and Vodafone variants of this device apart from some on-device software differences and variations in the tariffs. At the time of writing T-Mobile has the lead on pricing.

Not everyone needs a high speed Internet connection like that provided by this modem, but if you do, the USB plug and play option beats a PC Card hands down.