Use phone over Wi-Fi?

[1magine]

airibis,
i am very interested in this skype service since i am paying $60 a month for my phone plan.
what you wrote is very detailed but can you go further into detail please? im illiterate
will skype work in canada?
can i keep the same phone number? and if i go with skype can i pretty much drop my phone plan to the cheapest one possible since id be using skype all the time?
oh and one more question, does it take alot of data? i only get 1gb of data per month.
thanks!