What US state has telephone code 001504?

00 1 504 is the way that a telephone number in New Orleans, Louisiana, would be dialed. However, it is incorrect to call that "telephone code 001504." In quoting international telephone numbers, you should always omit the international access prefix (most commonly 00, but many countries use other prefixes) and give the number beginning with the plus symbol and the actual telephone country code, in this case +1 for North America (USA, Canada, etc.).

(The plus sign means "insert your international access prefix here." From a GSM mobile phone, you can enter the number in full international format, starting with the plus sign. The most common prefix is 00, but Japan uses 010, Australia uses 0011, and many other countries use different prefixes.)