Calling While On Roaming

I’ve recently had an interesting (and looooooooooong) conversation with my sister on phone calls, vs calls via an app, while roaming.

Well… I think it is a great idea for an post.

First things first.

What is roaming?

I will try to keep things simple, you can search on Wikipedia for details.

You have a mobile phone contract with a network provider. There are many network providers in the world; each one has a different mobile network.

The home of your network provider is called your “home network“. Any other network you connect to is called a “visitor network“. When you are on a Visitor Network you are roaming.

While roaming your normal tariffs do not apply and, depending on the laws (e.g. EU Roaming Regulations) and contracts between providers, you may start paying extra.

What is the difference between a normal phone call and calling via messaging apps?

While a lot of people call the two things “just making a phone call”, there is an important difference between a “real phone call” and using messaging apps like Google Duo, Telegram or WhatsApp (no preference just following the lexicographical order).

When you are making a real phone call, i.e. you are using the actual phone in your smartphone, your voice is transmitted via the mobile network (no data plan required), you are connected on, and routed towards the phone number you are using.
It is important to notice that this has nothing to do with any data plan you have or to the fact that you are connected to a WiFi network. A phone call depends solely on the phone network you are connected to. If your phone is connected to a WiFi network, but is not connected to the phone network, you cannot make a call. (I will not cover the case of operators with Call over WiFi, like AT&T or Google Fi, as it requires enabled smartphone and doesn’t work in all countries)
What you are going to pay is dependent solely on your voice plan. If you have a finite amount of minutes you can call for free up to this limit and you will start paying extra after you go over it.

When you are using a messaging app to make a call, i.e. you are not using the actual phone in your smartphone, your voice is transmitted via the Internet. This is called VOIP (Voice Over Internet Protocol).
It is important to notice that this has nothing to do with any voice plan you have or that you are connected to a phone network. These kind of phone calls can work with either a mobile network (data plan required) or via a WiFi network.
What you are going to pay is dependent solely on your data plan. If you are connected to a WiFi network you can call for free as much as you want, regardless to being connected to a mobile network. If you are connected only to a mobile network, and you have a finite amount of data in your plan (generally expressed in multiples of GBs or MBs), you can call for free up to when your phone reaches this data, not minutes, limit and you will start paying extra after you go over it.

So what is the difference when I’m roaming?

Here it really depends on your plan. If you have free minutes or free data use it as you prefer. I will focus on the case in which you don’t have them, or you have already ended them.

I will use the current (2020/01/31) Swisscom roaming costs as an example.

The cost of a normal phone call is 0.60 CHF per minute, while the cost of data is 4.90 CHF for the first 200 MB of traffic, which is 0.0245 CHF per MB.
Looking fast at the numbers you may think that a phone call is way cheaper than data. In this case you are making a mistake: you are comparing a cost per minute to a cost per MB.

How can I convert MB to Minutes?

Well, you can’t

But what you really want is…

How many MB are used for a Minute of call?

It depends on the bitrate, i.e. the number of bits that are transmitted per unit of time.
The bitrate depends on many factors (e.g. codec, encapsulation, …), but I promised I would have avoided details.

I will use data on WhatsApp that I was able to find.
I will use the worst case scenario: 64 kbps (64 Kilo bits per second), which means that 8 KB (or if you prefer ~0.008 MB) are needed for each second of the call.

So the answer to our question is:

0.48 MB per minute.

So how can I compare them?

Let’s compare them as cost per minute.

For a normal phone call, while roaming, we know the cost in our case 0.60 CHF per minute.
For a phone call via a messaging app the cost is ~0.012 CHF per minute (0.48 MB per minute multiplied by 0.0245 CHF per MB).

This may be not fair as in the contract we are considering you pay 4.90 CHF regardless of using the whole 200 MB or not.
In this case we can consider how long can you call with this 4.90 CHF.
With a normal phone call you can call for a bit more of 8 minutes, while with a call via a messaging app you can call for more than 6 hours and 48 minutes.

Conclusions

If you are roaming and you have a WiFi connection prefer using a messaging app, you will have no hard limits. Except for the time needed to sleep between two phone calls.

If you are roaming and you don’t have a WiFi connection.

First,

Check your voice and data roaming plan and run the number as we did above

Generally,

Prefer messaging apps

In our case normal phone calls were a good choice only if we were certain not to make more than 8 minutes of total calls.

I don’t know you, but, when I call my mom, it always takes more than 8 minutes

Carlo Bernashina