A number format for telephone numbers
Telephone numbers are not numbers, but Excel treats them as if they are (e.g. deleted leading 0). Excel isn't a database, but we all do it. Give us a specific 'number' format for telephone numbers so that Excel knows to leave the 'number' alone.
Sergei Baklan commented
IMHO, different phone number formats is the main issue which prevents to create universal one with leading zeroes. Otherwise that's not number formatting, that's converting to text.
If work with numbers you may use your own custom number format for phone numbers like +0(000)0000 000, depends on how many digits it shall be in it. That could Ctrl+1 plus Format Painter or better to create cell style.
Karl Gasson commented
Thomas K - it doesn't matter what the phone number format is, I want to be able to tell Excel 'this is a phone number leave it alone'
Thomas K commented
But what is a phone number format, considering it is different all over the world...