You can use Reason's vocoder, but it's a little widgety because Reason has no input option. Not even when rewired into Cubase. You can:
1) record vox, export to .wav, open wav in ReCycle, save as rex file to be played in Reason.
2) get the fantastic Orange Vocoder vst plugin. I've played with quite a few vocoders, and this one is both the best sounding and the easiest to use.
Unfortunately, nothing seems to come close to the power of Reason's vocoder. For this reason alone, I find myself frequently going the rex file way. I have tried a demo of NI's Vokator, but without some extensive manual studying, I was unable to do what I wanted. It looks fairly capable though, so maybe you should check it out. You might be smarter than me.