Modular phones have been hypothesized for years, with Phonebloks and Project Ara being the most popular concepts and just some shy experiments, like Fairphone 2, LG G5, Motorola Moto Z and Librem 5 inheriting part of the modular smartphone paradigm through replaceable boards, PCIe and other simple expansion mechanisms.
However, maybe due to the heavily proprietary nature of the extension stacks, and partly due to the small numbers of practical applications, with USB Type-C addons overcoming many expansion mechanisms, the modular aspects most of these were shortly forgotten and seldom repeated in newer models. What is not widely known about the PinePhone, however, is that the back of the motherboard exposes some pogo-pins (that is, elastic, spring-like expansion contacts that get physically compressed in the external rigid chassis when not needed) which can allow for easy expansion of the functionality of the PinePhone via hypothetical expansion boards.
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Modular phones have been hypothesized for years, with Phonebloks and Project Ara being the most popular concepts and just some shy experiments, like Fairphone 2, LG G5, Motorola Moto Z and Librem 5 inheriting part of the modular smartphone paradigm through replaceable boards, PCIe and other simple expansion mechanisms.

However, maybe due to the heavily proprietary nature of the extension stacks, and partly due to the small numbers of practical applications, with USB Type-C addons overcoming many expansion mechanisms, the modular aspects most of these were shortly forgotten and seldom repeated in newer models. What is not widely known about the PinePhone, however, is that the back of the motherboard exposes some pogo-pins (that is, elastic, spring-like expansion contacts that get physically compressed in the external rigid chassis when not needed) which can allow for easy expansion of the functionality of the PinePhone via hypothetical expansion boards.

Read more:

https://tuxphones.com/pinephone-modular-expansion-boards-pogo-pins-i2c/