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 +33 0 1 23 45... 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 (+33 123 456 789)