I'm getting a iPhone 6s from a friend. She is from Canada and uses bell. Can someone unlock it if it's not network unlocked?

I'm getting a iPhone 6s from a friend. She is from Canada and uses bell. Can someone unlock it if it's not network unlocked?

If it is locked, then you can only use it with certain plans. Bell Canada is in Ontario, which may present a problem using it in the US But maybe not. Since it is locked, ask your friend what services they allow with it. If you used a pre-paid plan or one of the smaller companies, then for sure, you will need an "unlocked" phone. Locked means that the manufacturer designed and sold it as restricted its use to certain phone companies.

Your friend will have to contact Bell in order to get it unlocked, only the network it is tied to can unlock it

Yes, either the carrier or a 3rd party service can get it unlocked.