I ́m considering changing from my present plan to prepaid; the reason is that I spend only 2-3 months at the time in Canada, followed by 2-3 months abroad, thus the plan turns out to be rather expensive. Would it be possible to pay out what I owe for the phone and change to prepaid?
Yep that's totally possible or you could put your plan on seasonal hold for 15/ month but all that does is reserve your phone number. Also remember you will lose all your boosters when you don't renew your baseplan if you plan to not renew while you're abroad.
Yes. It is possible to switch to prepaid from postpaid.
If you want to keep your number, open a prepaid account first and port/transfer your number. It will cancel your monthly plan and Koodo will send you a final bill including any remaining tab and overages if any.
But if you are in Canada only a couple months in the year, there is a cheaper service provider though.... ( I forgot which company)