To be honest, IMHO, the ideal would be an open, federated platform based on XMPP(or SIP) which supports sending text, voice/video call and also sending files. AFAIK, text/voice/video is already supported but I didn't find any client/server supporting sending images/audio and other files. (I found a draft for supporting such scenarios based on WebDAV, but apparently it is too new).

If that is supported properly, and the service is provided by at least a single server, I would jump on it and will try to encourage others to do so. XMPP is very close, but such an open platform is probably not commercially interesting for anybody to invest in.

I wonder what would happen if EMail was going to be invented these days! Your emails were probably limited to a single provider.