Signal is working on a way to sign up without a phone number. The feature has not yet been officially confirmed, and it is not yet known whether it will be available to all users or in what form.
Whether or not you can find someone based on their phone number is based on a user setting. Each person chooses whether or not they can be found by their phone number.
Go to Settings - Privacy - Phone number.
Really though, this is an excuse more than a roadblock.
I find people oddly resistant to an additional message app, yet they gleefully download a new app at every carpark they visit. People are odd.
Whether or not you can find someone based on their phone number is based on a user setting. Each person chooses whether or not they can be found by their phone number.
Go to Settings - Privacy - Phone number.
Really though, this is an excuse more than a roadblock.
I find people oddly resistant to an additional message app, yet they gleefully download a new app at every carpark they visit. People are odd.