(1) A provider of electronic communications networks, electronic communications services, associated facilities or associated services is encouraged to use the non-compulsory standards or specifications drawn up and published by the European Commission in accordance with Article 39 of the Directive for the provision of any or all of the following -

(a) services,

(b) technical interfaces, or

(c) network functions,

to the extent strictly necessary to ensure interoperability of services, end-to-end connectivity, facilitation of provider switching and portability of numbers and identifiers, and to improve freedom of choice for users.

(2) In the absence of publication of standards or specifications in accordance with Article 39(1) of the Directive, a provider is encouraged to implement standards or specifications adopted by the European standardisation organisations.