Wi-Fi Assist is a feature in iOS on the iPhone that potentially could improve internet access for apps and services. However, it comes at a cost and it could cost you money. Is it worth it?

Wi-Fi vs mobile or cellular data

A mobile phone can access the internet in two different ways. One is by using a wireless network and the other is by using the mobile phone network, in other words, mobile or cellular data. (It's called mobile data in some countries and cellular data in others.)

There is rarely any limit to the amount of data you can download and upload on a Wi-Fi connection these days, which makes them great for things like viewing photos online, and streaming music and videos. It is basically all-you-can-eat data with no worries. When there is a Wi-Fi network you can connect to, then the phone can send and receive as much data as it likes.

The same is usually not true of mobile or cellular data. Most people have a fixed limit one the amount of data they can use and this depends on the terms of the contract you signed up to with your phone service provider. It may be as little as 500 MB or as much as 10 GB. The higher the data allowance, the higher the charges on the phone service contract.

Having two different ways that an internet connection can be established is useful and when there is no Wi-Fi hotspot in range because it means you can still send and receive email, access the internet with a browser and use Maps and other apps that require internet access. They all use the mobile data connection when there is no Wi-Fi.

You have to be careful how much data is being used, because if you go over the limit set out in the contract, then extra fees may be applied and these may be expensive. It depends on the contract.

What is Wi-Fi Assist?

Wi-Fi Assist is a feature that chooses the best way to connect to the internet. If there is a great Wi-Fi network available, it will be used by the iPhone and apps to access the internet.

However, if the Wi-Fi signal is poor or if the internet connection via the Wi-Fi is poor, then mobile data is used because it will provide a better and faster connection.

This can be useful in situations where the signal varies or if you are walking around and the phone automatically switches from Wi-Fi to mobile data seamlessly and without the hassle of having to manually switch over. You always have the best possible internet connection.

Wi-Fi Assist is turned on by default and is well hidden in iOS. On the iPhone, go to Settings > Cellular or Settings > Mobile Data (the menu varies with the country).

There is a potential problem with Wi-Fi Assist and when the Wi-Fi is poor and the iPhone switches to mobile/cellular data, you could end up using quite a lot. In fact, you could go over your contract limit and this could incur additional charges on your phone bill.

This will obviously affect people with a low limit more than those with a high limit. The question is, is the convenience of a better connection worth the risk of going over your data limit?

Should you use Wi-Fi Assist?

If you plan to leave Wi-Fi Assist in its switched on default setting, you should keep an eye on the amount of mobile data the phone is using. If it uses a lot, you should switch off Wi-Fi Assist. In fact, if you have a low data limit on your phone contract, to play safe you should keep Wi-Fi Assist turned off all the time. Then it will not cause you to use more data than your allowance.

Apple has been sensible about this and it will not let apps that use a lot of data use mobile data with Wi-Fi Assist. For example, apps that stream music or video, or download large files may be prevented from using mobile data by Wi-Fi Assist. This will help avoid busting your data limit, but don't rely on it because it might not prevent every app from using data, just the obvious ones.

One thing you can do to prevent accidentally using too much data is to disable mobile data for apps that are unimportant. On the same screen as Wi-Fi Assist is a list of apps and you can choose which are allowed to use mobile/cellular data using the on/off switches.

It is a feature to experiment with and to be aware of the dangers of using too much data.