Calling London from Paris: Dial 00 44 20 XXXXXXX, Not Just 003344

You cannot dial a landline using only "003344." That string mixes France's exit code (00) and country code (33) with the UK's country code (44)—but omits the UK area code and local number.

Correct sequence from Paris (landline or mobile):

1. 00 – International access code (France/Europe).
2. 44 – UK country code.
3. 20 – London area code (drop the leading 0 from 020).
4. XXXXXXX – 8-digit local number.

Full example: 00 44 20 7123 4567

On mobile, you can replace 00 with +: +44 20 7123 4567. The "33" is France's country code—used when calling into France, not out of it.