1.If you add one single number to an existing number anywhere in the world…your call will NEVER get tru,the same happens if you take one number off.So just the amount of numbers needed.
2.Country codes are 1-2 and 3 digits,it varies depending on the amount of telephone lines in each country. Brazil 55(big)— Costa Rica 506(small)Russia 7 and USA 1 (huge)
3.Countries in Europe start whith 3 and 4 ,in America is 5,9 is in the middle east and so on. Cheers!!!