There is a powershell way also:
Create a file called speak.ps1
param([string]$inputText)
Add-Type –AssemblyName System.Speech
$synth = New-Object System.Speech.Synthesis.SpeechSynthesizer
$synth.Speak($inputText);
Then you can call it
.\speak.ps1 "I'm sorry Dave, I'm afraid I can't do that"