I think it would be really useful if you could synchronise Proton contacts from all Proton apps with the contacts on your mobile phone. And in both directions: so that I have all the contacts from my mobile phone on Proton, and all the contacts from Proton on my mobile phone. That way, I wouldn’t have to back up my contacts to iCloud, for example, and could back them up securely in Proton. But at the same time, I’d still have the contacts stored locally on my mobile phone so that I could easily use them for all messaging apps and the like.