Since you're in Canada, I don't think you have landline portability at all. Bell will probably let you keep your number since you'd just be moving it from a POTS line to VoIP on the same pair of wires, so it'd end up being switched in the same switch.
Having just managed to cancel my Vonage "service" this evening after trying for more than a month, I'd stay away from them. Now I'm using Primus Lingo which seems OK.
Regards,
John Levine snipped-for-privacy@iecc.com Primary Perpetrator of The Internet for Dummies, Information Superhighwayman wanna-be,