Our different ways of writing telephone numbers can lead to confusion. That's why in 1988 ITU set an international notation standard format.
This is the correct way to write telephone numbers:
+22 607 123 4567
The following formats are therefore discouraged:
- 0022 607 123 4567
- +22 (0)607 123 4567
- 0607 123 4567
- 123 4567
Akin to xkcd 1179: ISO 8601 about proper date format (entry on explain xkcd), this is promoting the ITU E.123 international notation for telephone numbers.
Because it's a notation that always works, no matter the constellation, skipping over national conventions, different national trunk prefixes (or not), remembering when to dial what and lastly different international call prefixes:
These prefixes are typically required only when dialling from a landline, while in GSM-compliant mobile phone (cell phone) systems, the symbol + before the destination country code may be used irrespective of the location of the telephone when dialing. The network operator provides the access codes automatically.
You know a counterexample where it doesn't work? Open an issue!