If you have an iPhone, Android phone, or another app phone, you don’t even need a cellular modem; you’ve already got one. Most app phones nowadays offer tethering, where the cellphone tunes into the Internet for the benefit of your laptop (or even your desktop computer). The phone connects to your laptop either with a USB cable or wirelessly (Bluetooth or WiFi).

The nice part is that you can get online almost anywhere there’s cellphone coverage. The less-nice part is that the connection isn’t always blazing fast, and you have to pay your cellphone company for the privilege. (It’s usually $20 or $30 on top of your regular monthly phone plan; for that, you’re allowed to send and receive 2 gigabytes of data each month. If you go over the limit, you pay overage fees. Good luck figuring that out.)

Here’s a typical example: Suppose you have an iPhone. You open Settings→General→Network→Personal Hotspot. You turn it on. You assign a password to your private little hotspot. The iPhone asks how you’ll be connecting to the phone; let’s say you tap Wi-Fi.

Now, on your laptop, you choose your iPhone’s name from the menulet. You enter your hotspot password (just this time—later, your laptop will remember), and presto: Your laptop is online. A bright blue “Personal Hotspot: 1 Connection” banner appears on your iPhone to remind you, and your menulet changes to become the International Symbol for Apple Tethering: .

Now, tethering eats up your phone’s battery like crazy; you’ll be lucky to get 3 hours out of it. So you probably shouldn’t count on watching Netflix on your laptop via your phone.

But for email, emergency Web checks, and other mobile crises, tethering is a convenient, useful feature. And when you’re on the road for a couple of weeks, it’s a heck of a lot cheaper than paying your hotel $13 a night for WiFi.