Personal Data. PTA shall adopt rules concerning arrangements for calling line identification. Article 52 Number portability Users of public telephone services, including mobile services, shall be able to retain their telephone numbers independently of the undertaking providing the service. This shall not, however, apply to the porting of numbers between fixed lines and mobile networks. PTA shall ensure that pricing for number portability is based on cost plus a reasonable premium. PTA may set more detailed rules1) on number portability and time limits in this connection and shall resolve disputes on its implementation. 1)Reg. 401/2001, cf. Reg. 840/2001, 508/2003 and 83/2004. Article 53 Carrier selection and pre-selection Undertakings with a significant market power for provision of connection to the public fixed line telephone network, shall enable their subscribers to access the services of any interconnected provider of public telephone services. The arrangements for such access may be either by the user dialling a carrier selection code on a call-by-call basis or by means of pre-selection, with a facility to override any preselected choice on a call-by-call basis by dialling a carrier selection code. User requirements for carrier selection or pre-selection on other networks or in other ways than provided for in the first paragraph shall be assessed by PTA on the basis of market analysis. If the conclusion of a market analysis is that competition is not effective, the Administration may impose obligations as provided for in Article 27. PTA shall ensure that prices for access and interconnection related to the supply of carrier selection and pre-selection shall be based on cost plus a reasonable premium. PTA may adopt rules1) concerning carrier selection and pre-selection. 1)Reg. 280/2002. Article 54 Integrity of the telephone network Undertakings providing publicly available telephone services must take all necessary measures aimed at ensuring uninterrupted access to the public telephone network and public telephone services, including emergency services. Users may not cause interruptions or disturbances to the telephone network. CHAPTER XI Digital broadcasting 24/34