I want to add a field (List text) to a content type, using as values the entries of another content type.
Should I use the References module?
No. Fields can be reused between any content type. In node's field administration page, use the existing field and values you attributes you set to that field will be available in both node types. But you can have different field labels and descriptions.
If you mean you have already created a field in another content type, and you want to add the same field (a List(text)) in another content type :
Normally the values will be copied.