Sure, you can move your Fido number to whichever company you go to.
However, looking at your usage, I doubt you'd be saving money with Speakout.
Using 250min /mth and 300 texts/mth will cost you $65 plus tax with Speakout, which is obviously more than the $50/mth you say you're paying with Fido.
I'd start shopping around this month, I know Bell and Telus are offering some decent plans this month (to entice the students going back to school), most likely Fido has a better plan for you, or even Rogers or Virgin.