| Flag | Code | Country | Time Difference (GMT) | Group | Comment | Internet Code |
 | 44 | Northern Ireland | 0 | UK | Ulster | uk |
 | 256 | UGANDA (Republic of) | 3 | BCW | | ug |
 | 380 | UKRAINE | 2 | | Formally part of USSR | ua |
 | 971 | UNITED ARAB EMIRATES | 4 | | | ae |
 | 44 | UNITED KINGDOM of GREAT BRITAIN and NORTHERN IRELAND | 0 | NATO, UK, BCW | England - Scotland - Wales - Northern Ireland | uk |
 | 1212 | UNITED STATES of AMERICA | -5 to -11 | NATO, USA | This is a hypothetical code - List of all codes | us |
 | 1340 | UNITED STATES VIRGIN ISLANDS | -4 | | | |
 | 878 | UPT | | GLOBAL | Universal Personal Telecommunication Service - Reserved code | |
 | 598 | URUGUAY (Eastern Republic of) | -3 | | | uy |
 | 998 | UZBEKISTAN (Republic of) | 5 | | Formally part of USSR | uz |