+42 → +420 · +421
Country Code 42 · Czechoslovakia
International telephone country code 42, assigned to Czechoslovakia (the Czech and Slovak Federal Republic) in the ITU numbering plan and retired in 1997, when the Czech Republic took +420 and Slovakia took +421.
Every country has a calling code you dial before the number. In the world plan kept by the International Telecommunication Union, Czechoslovakia's code was 42. In 1993 the country split into the Czech Republic and Slovakia, and for a few years both kept sharing 42. Then the plan's rule took over: new codes are given out three digits at a time. So 42 became 420 for the Czech Republic and 421 for Slovakia. Liechtenstein, once reached through Switzerland's 41, now has 423.
What it supports
An exact assigned code with a real job, printed by the ITU itself. CCITT Recommendation E.164 (1991) lists "Czech and Slovak Federal Republic 42," between Switzerland and Liechtenstein at 41 and Austria at 43, and states that "All spare country codes will be assigned on a three-digit basis." The ITU list of assigned codes (2016) shows 420 Czech Republic, 421 Slovak Republic, 423 Liechtenstein, and the rest of 422 to 429 spare.
What it does not
Not a code chosen for its digits: codes are handed out by world zone, so 41 and 43 sit right beside it. No hidden meaning in 420 beyond the three-digit rule. The 1997 switch date (28 February) comes from secondary sources; the ITU notice of the change was not found. Not IANA port 42 or any internet registry. Not the 420 objects elsewhere on this shelf. Not Adams.
ExactnessDesignation
Form42
UnitE.164 country code
Strengthhard
When1991 · 1997
Hung7 October 2026