Mobile data versus Wi‑Fi

By Martin Edwards

Published April 2017

Traditional telephones use wires and a network of exchanges to connect subscribers across the world. Any subscriber can call another by dialling their unique number. In return for this convenience and to pay for the upkeep of the infrastructure, telecoms companies charge for phone calls, usually by the minute.

Mobile phones partly replace wires with radio waves. A network of towers divides the land into ‘cells’ – hence the American word cellphone – with which nearby phones communicate. The practice of charging subscribers a per-minute rate remains, though many subscriptions offer a monthly quota of minutes for a fixed price that can work out better value.

Mobile data

In the nineties, ‘second generation’ or 2G technology made it possible to offer Internet access via these same radio waves. This brought websites and email – familiar aspects of computing – to mobile phones. Things really took off a decade later with the advent of so-called smartphones and faster 3G and 4G technology. Charging for this ‘mobile data’ use by the minute did not make sense, as it was to occur in frequent but intermittent and often very short bursts.

Instead, mobile data use is charged by the megabyte. In other words, subscribers pay for the quantity of information they receive or transmit, irrespective of when and for how long they do so. This is logical for telecoms companies, for technical reasons, but makes it harder for customers to comprehend what they’re spending. If your subscription includes 500 megabytes of mobile data per month, what does that mean in practice?

One can estimate that an email might be 20 kilobytes (20 thousandths of a megabyte) while a web page might be 500 kilobytes (half a megabyte) and a photo around two megabytes. The old saying ‘a picture is worth a thousand words’ is actually quite appropriate here! But remember that these are all estimates or averages. The point is, you can’t simply count what you use, like you could with minutes.

To complicate things, smartphones use mobile data for a whole range of things besides websites and email. How much data your iPhone uses when you get driving directions, for example, or say ‘hey Siri, will it rain tomorrow?’ — is anyone’s guess. And some mobile data use occurs ‘in the background’; that is, while your phone is idle in your pocket or by your bed. This allows the phone to know its location, keep its clock accurate, receive emails, update apps, and do other things you normally don’t think about.

Over time you’ll become familiar with how your daily mobile Internet use translates into megabytes. To help you, smartphones keep a count of how many megabytes you use; you can usually find this in the settings app. Your provider (e.g. Vodafone or O2) also counts your mobile data use, which you can see by logging into their website or using their app. You should also find out what happens when you reach your monthly quota: does your provider prevent you exceeding it, or start charging by the megabyte for any excess use? (And if so, how much? It may be surprisingly high.)


Another computing development of the nineties, Wi‑Fi also offers wireless Internet access via radio waves, but over much shorter distances — in the order of metres. Wi‑Fi tends to exist where a landline broadband subscription is shared among laptops within a building or campus, but smartphones can use it too.

As an extension of an existing broadband service, Wi‑Fi in homes, offices and universities is almost always free (some home broadband subscriptions do have a monthly limit, but usually much higher than that of mobile subscriptions). In hotels, railway stations and other commercial environments, Wi‑Fi is usually free, but some places may charge a small amount. If there is a charge, this is made obvious when you connect, so you can decide whether or not to proceed.

In any case, Wi‑Fi is a great alternative to mobile data. Once connected, for as long as you remain in range, your phone will use Wi‑Fi in preference to mobile data, so you are free to visit loads of websites – and even do data-intensive tasks like watching videos – without worrying about your monthly mobile data limit.

Note that unlike for mobile data, you must explicitly instruct your phone to connect to a Wi‑Fi network.

Privacy and security

It’s important to know that when you use Wi‑Fi, you’re putting a certain trust in whoever operates the network. This is because it’s possible to create rogue networks — for example to capture or change information you send and receive. In some situations it may also be possible for anyone using the same Wi‑Fi to eavesdrop on what you are doing.

The safest place to use Wi‑Fi is usually at home. Your network has a password known only to you and your family (and any guests you choose). You trust your router because it’s connected directly to your broadband provider and to the best of your knowledge has not been compromised.

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