Hi #[2]! Unfortunately we haven't implemented mentions yet. We render them from other clients but they don't get encoded correctly when you post from Nos. It's at the top of my wish list!

The UNS system is totally optional. You can still put whatever username you want on your profile and use any NIP-05 provider, no phone number required. Personally I want to see Nostr support multiple NIP-05 identifiers so I can keep the one from my personal domain and add UNS on top of it.