Some smartphone prototypes from Xiaomi are in circulation that are equipped with an M bayonet. Thus, corresponding Leica lenses can be attached and used.
Xiaomi 12S Ultra Concept with M-mount.
These are known to be designed for full-frame, while the prototype, however, "only" has a Type 1" sensor - it is a special variant of the Xiaomi 12S Ultra that was introduced in the summer. Whether the Xiaomi 12S Ultra "concept" smartphone will ever go on sale is questionable, though. At least, there are about 10 working examples that were distributed to photographers as proofs of concept.
Interestingly, the optics are not placed on an existing camera module - as is usually the case with attachment lenses (which means double optics with a corresponding loss of light), but on this device Xiaomi has placed an additional, bare sensor in the middle of the camera section and rearranged the array of the other camera modules a bit for this purpose. The choice of the M-mount naturally goes back to the technology partner Leica, but it is advantageous that the flange focal distance is relatively short (27.8mm) and the lenses are quite compact. Since the image sensor is directly behind a protective glass surface in the concept phone, an adapter ring still has to be used in addition to the optics to get the required distance for the flange focal length.
Perhaps one or the other remembers the Lens-style Cameras Sony QX100 / QX10 from 2013. There, the setup looked similar, but the concept was completely different. An optic was strapped to a smartphone, but this was optional, because the image sensor was built into the lens, and the phone (display) was only needed for the preview. Since communication was via WLAN, the filming lens could also be operated separately from the smartphone. This type of camera did not catch on at the time.
Since all kinds of M lenses can be used on the Xiaomi 12S Ultra Concept, the system is much more flexible and thanks to the conventional camera modules on board, the interchangeable lenses are also optional. If you just want to be on the go with the phone without better camera features, you can simply leave them at home. We could well imagine that such a device could basically meet with interest, especially among those who still have old M lenses in their closet.