When your phone is in airplane mode, it is effectively "de-registered" from the cellular network, meaning the radio waves containing a text message cannot reach your device. If someone sends you a standard SMS (text message), it is not lost; instead, it is stored in a holding queue on your mobile carrier's servers (specifically at the Short Message Service Center, or SMSC). Once you turn airplane mode off and your phone "pings" a cell tower to re-establish a connection, the carrier’s server recognizes your device is active and "pushes" the queued messages to your phone. However, there is a Time-to-Live (TTL) limit; if your phone stays off or in airplane mode for too long (typically more than 48 to 72 hours depending on the carrier), the server may expire the message and discard it. For data-based messages like iMessage or WhatsApp, the process is similar but handled by Apple or Meta's servers, which generally have longer "hold" periods than traditional SMS.