[Arathorn]

Matrix is an open network like Email or the Web. So if you use a "free" server, it means you've selected a public server like matrix.org or privacytools.io or whoever. These servers are hosted philanthropically for the benefit of the overall network (e.g. Matrix.org's hosting is paid for via Patreon: http://patreon.com/matrixdotorg).

If enough organisations run their own servers and make them available to their users for free, then you could indeed support the online billions. Instead, much like email, we already see a mix of free services (the equivalent of hotmail, gmail etc) and paid services (the equivalent of g-suite, protonmail, etc).