Hi Matthew,
NetTalk does not support the SFTP protocol.
I'm not sure what you feel is unsafe about SSL. It's the network standard for secure transfers - all commercial sites on the internet use it to protect financial transactions, credit cards, and so on.
so yes, I recommend SSL for uploading / and downloading files that must be secure. Of course, coupling that with logins makes it even more secure - in the sense that you limit _who_ can download files etc.
cheers
Bruce