Offline SMS is essentially access to messaging functionality when a user doesn't have an active internet connection. However, the term "offline SMS" can be misleading, as standard SMS (Short Message Service) always operates without an internet connection, relying instead on the cellular network. The common usage of "offline SMS" usually refers to using SMS as a fallback when IP-based messaging services (like iMessage, WhatsApp, or other chat apps) cannot connect to the internet.
Therefore, "offline SMS" can be interpreted in two ways:
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Traditional SMS Functionality: This is the baseline understanding. SMS inherently works independently of an internet connection. It utilizes the cellular network's signaling channels for transmission.
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Fallback for Internet-Based Messaging: When apps like WhatsApp, Facebook Messenger, Signal, or iMessage can't connect to the internet (Wi-Fi or cellular data), they may resort to sending messages as regular SMS texts if the user has enabled this option. This allows for continued communication, albeit with the limitations of SMS (e.g., lack of rich media, shorter message length, potential charges).
In summary, standard SMS is always "offline" in the sense that it doesn't need an internet connection. The term "offline SMS" is often used in the context of IP-based messaging apps reverting to traditional SMS when an internet connection is unavailable.
