What is an eSIM and should you travel with one?

But first, who needs an eSIM? If you are on a mobile phone contract with one of Australia's biggest network providers then they will usually have international roaming available for a set daily fee.

Telstra charges about $10 per day for unlimited calls and SMS plus a couple of GBs of data, so if that price looks right to you, you don't need to look into an eSIM.

But not all plans are created equal. If you are on a pre-paid or pay-as-you-go mobile plan, rates can be way more expensive. Take, for instance, Telstra, which charges $3 per MB of data for PAYG, and it uses about 3.75 MB/minute for a one-way standard-definition video call, so you can see how the cost could stack up.

If you are on a plan such as this, or use another provider that doesn't include roaming or their roaming data is expensive, you might want to look at an eSIM.

You can buy from hundreds of different brands online, but it's wise to read some reviews to work out which one is right for you.

Tech Guide editor Stephen Fenech says an eSIM is "a little chip inside your phone that can contain all the information that would normally be contained on the little plastic SIM that you insert manually into the phone".

"SIM stands for subscriber identity module. It identifies you and your device on the network. The eSIM allows you to have your information but without having to use the actual plastic SIM card," Fenech explains.

For travellers, this is a "huge advantage" because you're able to keep your own SIM card in your device and set up an eSIM to use while you're travelling overseas. This also allows you to keep your phone number while travelling.

The catch is, most eSIMS are data only, and if you have one of those, you can't call out or send SMSes, but you can receive calls and SMS on your physical SIM via your old number. In this instance, your eSIM will be used for data only. However, some eSIM providers will include a new number in the service.

Most eSIMs can be purchased days or even weeks before you plan to travel, and set up the day before you fly - or even at the airport.

You need a stable Wi-Fi or data connection to set up the eSIM (so you might choose to do it at home), and once you have done so, it automatically connects at your destination - no waiting in a queue to purchase a physical SIM at the airport.

But there is a limitation: not all phones are compatible with eSIM, so make sure you check your phone is compatible before you purchase a plan.

Zapme founder and CEO, Scott King, recommends using esimradar.com to compare the eSIMs available for your destination.

He says cheaper isn't always better: look at the speeds on offer. You'll need at least 512 MB per second (upload and download) for a good user experience.