How Non-SIM Solutions Process SMS Without SIM Cards

How SMS Is Delivered Without a Physical SIM Card

A SIM card is the most common way to receive and process SMS, but it is not the only option. Mobile networks can replace it with either embedded components or special software, and the internet provides software solutions. Both types offer similar quality and follow roughly the same algorithms. However, a few key differences matter when discussing data security and network interoperability.

Technologies Replacing SIM Cards

Popular technologies that can receive and send SMS fall into two groups: those based on mobile networks and those based on an internet connection. Both achieve the same result as the physical SIM, but they can boast the following advantages mostly related to management and maintenance:

• No risk of physical damage or loss. Software can be reinstalled without harming your account or number. 
• Instant launch and replacement. A user can easily replace, add, or deactivate a number. 
• Easy scalability. Multiple numbers can be held on the same carrier or in the same app.
• Low costs. Non-physical solutions cost a fraction of the price of SIM cards.

In general, many experts consider these solutions more convenient, safer, cheaper, and, thus, smarter than SIMs.

SIM Equivalents Based on Mobile Networks 

This category naturally derives from the original plastic SIMs. Depending on the device’s hardware, it can use one of the following solutions:

• iSIM and eSIM. The system uses the device’s processor in the first case or a dedicated chip in the second. This technology supports the number and maintains security at the hardware level.
• eSIM adapters. This gadget bridges a classic phone with a SIM slot and standard eSIM virtual profiles using an eSIM chip.
• SoftSIM. A solution that does not use any hardware and relies on software only.

These alternatives use either software or non-removable hardware primarily integrated for other purposes. Thus, they don’t need a separate SIM card.

SIM Alternatives Based on an Internet Connection

This is a more advanced stage of phone number evolution, processing SMS over the internet at several stages of delivery. The most common options include:

• Permanent virtual numbers. These are long-term cloud numbers, mostly based on VoIP technology. This version is used for SMS-based client support, promotional messages, and interdepartmental communications.
• Temporary numbers. These are also cloud solutions. You can use a GetTempNumber service or a similar option for one-time verification during account registration.
• Messengers and call apps supporting OTT. WhatsApp, Viber, and similar solutions allow clients to link their existing numbers to receive SMS.
• A2P platforms with cloud SMS gateways. Automated software for receiving SMS, 2FA, and chatbots for bulk messaging, which has external APIs for integration with internet telephony. 

These solutions run on servers and require no special infrastructure on the user’s side.

How SMS Is Processed in Mobile Networks

iSIMs, eSIMs, and SoftSIMs look like physical SIM cards in mobile networks, and they are processed in approximately the same way:

1. Device authentication via the Ki stored in hardware (eSIM, eSIM adapter, or iSIM) or software (SoftSIM).
2. Creating a PDU packet.
3. Redirecting the packet to an AMF or MME managing node, as in the case of a regular SIM. 
4. Transferring data to the SMS Center.
5. Searching for the receiver’s number (MSISDN) in providers’ databases and sending the packet.
6. If you and your receiver use different providers, your provider sends the PDU packet through the SS7 or HTTP/2 gateway.
7. Checking if the receiver’s device is active by sending a paging signal.
8. Sending the encrypted message via downlink.
9. Decrypting the SMS, displaying the message, and sending an acknowledgment.

Such a procedure maintains essentially the same security level as a standard SIM because encryption and decryption are processed within the device.

How SMS Is Processed in Internet Clouds

To transfer an SMS through the internet, the system intercepts it in the telecom core. The subsequent network route of the message is as follows:

1. Encrypting a PDU message.
2. Sending it directly to the SMS Center, without managing nodes.
3. Checking a receiver’s number type (cloud or mobile network).
4. If it belongs to a cloud or VoIP provider, the system transfers it to the IP gateway.
5. If the virtual number is temporary, the system can use a SIM bank or an alternative solution to receive and forward the incoming data.
6. Once read, the data is reformatted into JSON or XML, a standard for the internet.
7. The system detects the current user’s status and builds a route to the user’s server.
8. Sending the message to the client through a REST API (server integration), WebSockets (browser), or push notifications (mobile app).
9. Accepting the message and sending a delivery receipt to the sender.

In most cases, these steps take minimal time, regardless of the network type or device involved. However, a hybrid route (from VoIP to a mobile network or vice versa) is more vulnerable than a mobile-only or VoIP-only solution.