Which mobile clients support this?
Discussion
You mean mobile webapps or native apps?
Native.
Amethyst and Yana that I know of. But those support Amber natively (offline) without the need for NIP46 remote signing, since the apps are on the same device.
The real benefit is that you can sign in to mobile and desktop webapps (on the same or different devices) using Amber's NIP46 signer.