Using a computer software to speak for you from your typed inputs?

[Ant]

For those who can't talk (well like impediments), do you use a talking
computer software to speak from your typings over the phones?

If so, then what do you use (freewares -- no time limited trials) in
Windows XP SP3 (mostly), Mac OS X v10.8.5, and Linux/Debian (stable)? Do
they work well for like job interviews, support, etc. with technical
computer terms? I know there are human speaker services online, but
there are sometimes I have private data I do not want to share with
others hence why I want my computer to the phone receiver directly.

Thank you in advance. :)
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