And vice versa?
Obviously this only applies when the line rental and the DSL service are provided by different companies (an SMPF situation), but would the line rental/ phone provider (e.g. Primus Saver) have access to which company provides the DSL service (e.g. Zen). Or if the DSL is provided via BT Wholesale, would they just know that? Likewise what would they know (if anything) about an FTTC provider?
The same goes for DSL providers - do they have access to who provides the phone service?