How to cannonicate numbers in international form

Joachim Breitner mail at
Thu Jul 17 22:45:49 CEST 2008


Am Donnerstag, den 17.07.2008, 22:14 +0200 schrieb Tilman Baumann:
> > In most cases, just a simple "n last digits match" test would be
> > sufficient. That's what all the usual phones do anyway, and false
> > matches are very rare. But hey, we can be more sophisticated :-)
> But way resort to such methods if the only reason is some crazy corner  
> case?

For me, it’s not a corner case: I just don’t want to read phone numbers
such as +49703212345 in my address book, where I have to look closely
where the area code starts and ends, so as a user, I expect my phone to
know that I the call I made to 0703212345 (dialed manually) is actually
to the person with the number +49703212345 or even 07032/12345 in the
contact list.

Do you disagree here already, or is this still a valid expectation?

Then, going to the question of implementation, I see three options:
 A) Having the user specify the details how he interprets phone numbers
(mostly, the country code prefix, I guess). Then the phone can fully
qualify every incomplete it sees for a reliable comparison (not for
display, though), and for reliable use of the phonebook in foreign
 B) Do not expect the user to enter anything, and do „best guess“
matches. Here we have two alternatives:
 B1) Have code that handle the various specialities around the world to
understand various number themes.
 B2) Compare the last n (maybe 7) digits, and leave it to the user to
use fully qualified phone numbers when he encounters an (unlikely)

I think A) is not good because it needs user intervention, and B1) is
too complicated – so that’s why :-)

> > By the way, I don't think requiring people to enter canonical numbers
> > is a good idea. When you travel, you often enough get numbers that
> > work if you dial them locally "as is", but you may not necessarily
> > have a good enough understanding of the local numbering plan to turn
> > them into fully qualified numbers.
> Well, if you (as a user) can not provide these data (because you don't  
> understand it) you just have to live without the benefits. No big loss.

I think it is a big loss. Especially those users who can not provide the
data (becaus they don’t care any mostly stay in one country) are the
ones that will expect their phone features to work without having to
type "+49" before every call.

(I’d like to back my claims with code, but MokoMakefile is still
compiling – since yesterday).

Joachim Breitner
  e-Mail: mail at
  ICQ#: 74513189
  Jabber-ID: nomeata at
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