I agree with Richard 12. Although I have personally bought one or two handsets outside of carrier shops, I can vouch for my friends and most people I know in France who typically go to their carrier shop when they want to change phones.
And if they want to change carrier, they go to the new carrier shop and make the deal, getting a new phone out of it as well.
Buying a phone without a carrier contract is not all that common in my relations, although it is not unheard of, given the number of prepaid phone refills on sale next to cashiers desks in every supermarket/gas station.
So I'm guessing that, in France at least, there is a substantial share of people who go to their carrier for their handset model replacement, and a non-negligeable share of people who buy outside of carrier shops (maybe secondhand as well) and use prepaid SIMMs or something like that.
Another point that is gaining in importance is the online secondhand market (Ebay, I guess, but Leboncoin is seriously gaining in activity as well). That has to have an impact on carrier sales.