Dual SIM mobile phones are nothing new. We've had them in some form since 2000. Everything from a basic Nokia or Doro, to top-end Android smartphones have been available in Single SIM or Dual SIM versions.

If you haven't seen one, it's simply a second slot for a second SIM card. This SIM can be on a different network, and will have a different mobile number.

Dual SIM phones can be really useful. Users that require separate work and personal numbers can elect to run both from one device. Also, people that regularly travel to other countries can benefit from having two SIMs - one UK SIM and one Spanish SIM for example.

The only major manufacturer that didn't release a phone with two SIM slots was Apple. However, the iPhone XS, XS Max & XR, released in 2018, were the first iPhone's to support two SIMs. The phone still has just one SIM slot, for the primary SIM. A second SIM can be activated and used electronically, without the need for a physical SIM card.

This is called an eSIM, which stands for embedded SIM card. A small chip inside the phone controls this function entirely. The information on an eSIM is rewritable, which means that the user can still change their number, network provider or data plan.

In 2017, Google released the Pixel 2, which was the first phone with eSIM technology. The Motorola Razr (2019 edition) was the first and so far the only phone to support eSIM only. It does not have a physical SIM slot.

In the digital age, it begs the question - why have a physical SIM card at all? Digital products and simply more flexible, convenient, reliable and efficient than physical products in most cases. No SIM slot means more space inside the phone for a bigger battery or other technology. It's also better for water resistance. Your Apple Watch uses e-SIM only, why not your iPhone?

Our current cellular systems and infrastructure are designed around SIM card technology. These systems are complex and universal, so they take a long time to update, especially in this case - it's a lot of work, there's no huge financial incentive, and the current system works just fine.

Most of our UK networks support eSIM technology, but most networks in countries such as China and India don't yet. Phones are sold globally, and need to be compatible with as many networks as possible.

No one company change the status quo by itself. Henning Schulzrinne, a professor of computer science, said that SIM cards are "a good example of an interdependent system that makes it difficult for anybody to change until everybody changes."

We must also consider the Mobile Networks themselves (EE, O2, Vodafone etc.), who can maintain a much closer bond with their customers, who rely on their physical products to make their devices work.

Physical SIM cards are actually a very secure way for the user to authenticate with the network - perhaps more so than digital SIMs, because they cannot be cloned, stolen or hacked.

Another advantage of physical SIM cards is that if you break your phone, you can swap your SIM into a spare phone as a quick and temporary solution.

So you can clearly see why we haven't yet transitioned to eSIMs exclusively.

In time, networks will adapt, the technological infrastructure will catch up, and we will manage our SIM plans through an app. Buying, activating and fiddling around with plastic SIM cards in fragile little trays will be a thing of the past that the children of today will never understand.

Gotten a SIM card jammed inside your phone? We can help.