I use Audacity to prepare the sample as I said, which, for example, I'm using an old telephone error message saying all the circuits are busy. I'll cut out the dail tone at the start and the rest of the clip so that I only have the phrase "We're sorry, all circuits are busy now"
though the whole phrases is, "BEEP BOOP BEEP, We're sorry, all circuits are busy now. Will you please try your call again later."
I do that cutting in Audacity.
From there, within FL Studio I use a combination of two plugins called Fruity Slicer (which does what you think it does, you use it to split sound files into slices, in this case I make each word a slice sometimes syllables a slice for precise timing). Fruity Slicer lets you play your slices like any other instrument. You basically are assigning slices to piano keys.
For scratching and time manipulation I use a plugin called WaveTraveler on the prepared samples.