Do you need a calendar that is independent of email?

So, the other day I was DMing on Twitter and the converseation led to a phone meeting. We both exchanged numbers but there was no easy way to add this as a meeting to a calendar. Then I realized this is true of Whatsapp as well. Is there any merit to building a calendar app that can work with any id ? Not just be married to your email address ?

For instance I should be able to just say meet with this <handle> at <time> and the app sends reminders to me and the handle accordingly. Just that the handle need not be an email address, could be a phone number, a twitter handle as well.