Mobile phone jammers
"The legality of jamming, has been discussed on several instances in the context of the R&TTE (1999/5/EC) and the EMC Directives (89/336/EEC). These discussions have made clear that Member States neither permit nor wish to permit radio communications to be disrupted by jamming devices operated by members of the public.
It is not possible to construct jammers that comply with R&TTE or the EMC Directives. Such devices cannot therefore be legally placed on the market within the Community for use under these Directives.
Therefore, where such products claim compliance with the R&TTE or the EMC Directive, Member States' market surveillance authorities are under an obligation to take them from the market under the provisions of those Directives and to notify such actions to the Commission."
(2005, http://ec.europa.eu/enterprise/rtte/jammers.htm )
National and international law limits the installation of mobile phone blocking systems. Still, for prisons there is a certain general policy of tolerance because of the security risks related to the unauthorized use of mobile phones. This has to be looked into per country.