This is a question that quite often crops up, usually from potential customers. Whilst it may seem an odd requirement, people often ask if multiple phone numbers can be assigned to a single SIM card. The short answer is no, it’s not possible for a SIM card to have two or more numbers.
Fortunately, there are alternative solutions that allow you to make use of multiple phone numbers so read on.
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Why can’t I have a single SIM card with two numbers?
SIM cards were first introduced along with GSM (the technology used to power the modern mobile phone network infrastructure) way back in the 1990s (thirty years ago!). Back then, the concept of needing to have multiple phone numbers attached to a single handset was practically unthought of. As such, the technology just wasn’t designed to support it.
A SIM card holds a unique identification number known as an IMSI. It’s used to allow the SIM card to identify itself (and therefore, you the subscriber, or customer) to the network. Once the SIM card has been identified, the network is able to look up which (single!) mobile phone number belongs to it.
Each GSM handset needs to be compatible with each GSM network and SIM card around the World. For this reason, it’s not practical to try to retrofit the ability to assign multiple phone numbers to a single IMSI. Hence, why one SIM card can only be associated with one mobile number at any particular time.
Why you might need two or more mobile numbers
Although it’s easy to see why one number would have been sufficient 30 years ago, it’s also easy to see that things have moved on and there are now legitimate reasons to have multiple mobile numbers.
Most employees for example will have a company mobile phone, as well as their personal handset. This is because it’s unlikely they’ll want to share their personal contact number with colleagues, customers, and suppliers (not to mention having it published on company websites or in the media!)
Likewise, most small business owners like to keep their personal number separate from work. Not only are there times when you might prefer to avoid business calls, but should the owner choose to sell the business, they’ll want to sell the business mobile number along with it, while keeping their personal number for themselves.
Solutions to have multiple numbers on one phone
Dual-SIM phones
Since we’ve established that one SIM card can only have one number, the obvious solution is to put multiple SIM cards in one handset.
Luckily, there are a wide range of phones on the market that allow more than one SIM card to be installed. Most of these allow two SIM cards to be installed at the same time, hence they’re referred to as dual-SIM handsets. At the moment, the only phones on the market that are dual-SIM capable are Android devices. Apple don’t manufacture any iPhones that can take more than one physical SIM card (they do make iPhones with an eSIM however).
How Dual-SIM phones work
You simply insert both SIMs into the SIM tray and the phone will recognise that it has two SIMs and therefore two mobile phone numbers. Often, installing a second SIM means you’ll need to sacrifice the ability to have a MicroSD card installed, as the slot for the second SIM card is the same slot that’s used for the MicroSD card. Fortunately, the amount of in-built storage on modern phones is sufficient for most people, meaning that a microSD card is never needed.
Once both SIM cards are installed, it’s very much like having two phones but only needing to carry around one. When you make an outgoing call, the phone will ask you which SIM card (i.e. which phone number) you want to use to make the call and you simply choose one. When anyone calls or texts either of your numbers, the phone will ring or receive the text in the usual way and will display which SIM/mobile number the call or text was intended for.
It’s also possible to fine-tune the phone’s behavior, such that a specific SIM card is always used for outgoing calls and texts. You can also designate a certain SIM card to be used for data purposes. For example, if you have a large 30GB data allowance on your Smarty SIM and only a 5GB package on your Vodafone SIM, you can tell the phone to always use the Smarty SIM when accessing the Internet.
Phones with an eSIM
In recent years, a number of phones have been released to the market that come with an integrated eSIM. An eSIM is a microchip that’s built into the phone, that’s capable of behaving like a regular SIM card. This means that it’s possible to install a regular SIM card into the phone, and also make use of the phone’s eSIM at the same time.
Using a regular SIM and an eSIM concurrently means that the phone will provide more or less the same functions as a dual-SIM phone with both SIM cards installed. Examples of phones with an eSIM module are the iPhone XS, the iPhone XR, and the Samsung Galaxy S22.
The main difference between a dual-SIM phone and a phone with an eSIM is that the latter will only work with networks that specifically support eSIM devices. In contrast, dual-SIM phones are network-agnostic and will work with providers across the board.
Call diversion and call forwarding
If you only ever wish to receive calls from multiple numbers and are content to make all your outgoing calls from a single number, then an easy solution is to use call-forwarding.
Simply put, you can purchase a new number (landline, mobile, non-geographic, etc) from a third-party telecom provider and ask them to forward all calls to your mobile number. For example, if you have a small business and don’t wish to advertise your personal mobile number, you could purchase a freephone 0800 number and ask the provider to divert all calls to your personal number. This way, your customers will only ever have your 0800 number whilst your personal mobile number remains a secret. If you ever choose to sell the business or take on an employee to fulfill your role, the business number can just be diverted to someone else instead. If you take this route, you probably want to disable outgoing caller ID so that if you need to return a call from your mobile, your personal number isn’t accidentally divulged.
Summary
Whilst it’s not possible to assign more than one number to a single SIM card, there are other options if you need to have a range of phone numbers. If you’re in the market for a new handset and would be happy with an Android device, then your best bet is to buy a dual-SIM phone and make use of two SIM cards.
If you prefer to use an Apple iPhone, make sure it has an eSIM module and that you’re on a network capable of supporting eSIM devices. This way you can have one physical SIM with one mobile number and an eSIM with a second number.
If you’re not ready to change your phone and your current handset isn’t dual-SIM or eSIM capable, then a quick solution is to purchase an additional number and forward it to your existing mobile number.