E.164 defines an international public telecommunication numbering structure. In an interface, a leading + and country code make the intended plan clearer.
Separate display from structure
Spaces, parentheses and hyphens aid reading, while the canonical number structure is defined by digits and a country calling code.
Know the geographic length limit
The February 2026 ITU-T E.164 sets a maximum of 15 digits for international numbers in geographic areas. The leading + is notation, not one of those digits; other E.164 number categories have their own structures.
Avoid guessing from local input
Without a country context, a national-looking number may be ambiguous. Ask for the region instead of silently inventing one.
Validation is not reachability
A valid pattern means a range is recognized; it does not prove a number is assigned or can currently receive a call.
One drama example, two displays
The Ofcom drama range lets us show a UK conversion without exposing a customer number. This is a UK example, not a universal rule for stripping zeroes.
UK national display
Example: 020 7946 0018
Purpose: Readable inside the UK plan
International display
Example: +44 20 7946 0018
Purpose: Country code plus national number
Compact international string
Example: +442079460018
Purpose: No display spaces
Incorrect UK conversion
Example: +44 020 7946 0018
Purpose: Retains the UK national trunk prefix
Formatting does not establish reachability. Other plans can retain significant leading zeroes, so apply their rules rather than copying the UK transformation.