I was listening to a Spanish-language radio station on my commute this morning, and in giving a phone number, the "disc jockey" said "tres veintitres" for "323". Why? "tres dos tres" is shorter. Is it just because it "sounds better" or what's the reason?
It's quite usual, to group digits arbitrarly when pronouncing phone numbers. And in this case, I find it natural, I'd probably pronounce it in that way: "tres veintitrés" sounds to me more neat and clear than "tres dos tres". True, the later is shorter, but it also can be slightly more confusing (in particular, "dos" sometimes -perhaps not here- can be confused with "doce").
Consider the case of years: "1978" for you is nineteen seventy eight, which for me in Chile is mil nueve setenta y ocho ("thousand and nine and seventy eight ").
Why none of us says one-nine-seven-eight (the shortest) or one thousand nine hundred and seventy eight (the proper)?
We need to group units into manageable pieces by both memory as phonics. Tres-dos-tres involves memorizing 3 units. Tres-veintitrés involves memorizing 2. The time loss talking is minimal compared to the memory won (one-third).
This is not a feature of the Spanish language but of cognition in general ("chunking").
I disagree with the answer accepted, although for some specific cases might be right.
First of all he is asking about a telephone number. We must remeber that each country, and even in some cases, different states, have different phone numbers convention, see here
In the case the radio was Spanish (from Spain), our convention is to say the numbers in Madrid 91 (province prefix) XXX - XX - XX
For my home's telephone number is say, something like ninety one, one two three, zero five, twenty two. In the previous one I changed a little.
Second, a famous radio called Los Cuarenta Principales (40), play with their name and number, since their number is 91 X 39 40 40.
Radio is an entirely auditory experience. I would suggest the purpose is primarily to give a boring telephone in a way that sounds more interesting and much more memorable. I think it is accomplished here by changing the rhythm and emphasizing the accent on
tres. Besides that I think the economy of saving one syllable is made up by not having the extra space between the three words (numerals) individually.