A telephone company can experience problems when large numbers of callers attempt to use the system at the same time. This generally only happens in exceptional circumstances such as a disaster or national emergency, but can result in some calls not going through at all. The United States has the Government Emergency Telecommunications Service and Nationwide Wireless Priority Service, and the United Kingdom(UK) has the Government Telephone Preference Scheme and ACCOLC to allow official calls to go through reliably in emergencies.