Because right now, Signal can use your contact list on the device to get your signal contacts. If you replace a phone number with a username, there will be no w

Because right now, Signal can use your contact list on the device to get your signal contacts. If you replace a phone number with a username, there will be no way to match signal's user to your contact without: - Having a server to hold your contacts - Or having signal app to maintain contact list and sync it across devices