[blahedo]

It's because if it's out of order, your "partial interpretation so far" in your head gets messed up. A relative of mine pulls a version of this in English (that I find hilarious): in American English we usually read phone numbers one digit at a time, but sometimes group pairs of digits, and it doesn't really matter because "forty five" and "four five" present in the same order. Their phone number has a 1 in it, so to prank people that are writing down or typing the number they read it as (numbers made up, but the effect is):

   five
   six
   seven
   four
   -teen

...

and then cracks up. I cracked up when it was done to me, although apparently not everyone finds it so funny. ;)

[BrandoElFollito]

In France we read our numbers in pairs: 01 23 45 67 89. The initial zero is complicated, it is a butchered-up solution when we were transitioning the numbers and in an international context one never knows whether to say [phone]... or +33 1 23 45... (the latter one is correct, though both will likely work). When you remove the zero in the international version, lots of systems will format the number by triplets, which seems to be more common in Europe ([phone])