The short answer is that there is no difference. 0207 number, a 0203 number or a 0208 number, just 020 numbers.
020 is the area code for London. The next part of the number then commences with a 3, 7 or 8, but that is not a component of the area code, it is just how they are referred to. But all three are precisely the same thing – London phone numbers. Ergo, it doesn’t matter whether you buy a virtual 0207, 0203 or 0208 number from us, it is still a 020 number and still a London phone number.
