13 Article 20 The Regulatory Board ensures that, commensurate with technological development and public network coverage, a directory enquiry service is provided by at least one public telecommunications operator as part of that operator’s individual license. The directory enquiry service is capable of being accessed to by all users in the Republic, including users that have prepaid for their telecommunications service. Public telecommunications operators that provide a directory enquiry service are permitted to charge for this. The charge is based on the costs of providing the directory enquiry service and a reasonable rate of return as determined by the Regulatory Board. Article 21 A public telecommunications operator provides public payphones in accordance with the terms of its license. The facilities and standards of all such payphones are laid down by the Minister having telecommunications in his/her attributions in a Ministerial decree. Article 22 Public telecommunications operators providing telecommunications networks and/or telecommunications services must comply with criteria set out in their licenses as to the quality of the networks and services they are providing. The Regulatory Board may at any time modify licenses issued to providers of telecommunications networks and services so as to change quality of service criteria. No modifications are made until: 1° a six months notice has been given to the relevant provider and; 2° the relevant provider has operated under its license for at least 18 months before notice is given. Criteria for measurement of quality of service together with the level of compensation which may be claimed by users if any quality measurement is not met are set out in a Ministerial decree. Quality of service criteria are the same or similar for the same or similar types of licenses. Information about quality of service as measured in accordance with the criteria are provided to the Regulatory Board as required by law. Failure to provide information is an offence punishable in accordance with the law. The Regulatory Board must in the first instance, issue an enforcement notice to any telecommunications network or service provider which fails to meet any quality of service criteria and specify the time within which the criteria have to be met. Continued failure to meet any service criteria specified in the enforcement notice may result in the Regulatory Board either: