911: nine one one vs. nine eleven [closed]
Solution 1:
How a car manufacturer names its models is more of a marketing preference than anything, but in general you'll find that the Porche model is the norm. Ask any schoolchild to read aloud the number "911" and you'll get "nine hundred and eleven", not "nine one one".
The telephone number 9-1-1 was, as you speculated, spelled out specifically to prevent people - particularly children - from getting confused looking for the "eleven" key on the telephone.
I have heard this anecdotally countless times, but I'm having a hard time finding an authoritative source. Closest I can come are various "history of 911" websites like this one:
Dr. Phil Shaenman, head of the U.S. Fire Administration's research department, authored a paper explaining that children should be taught to dial "nine-one-one," and not "nine-eleven." He pointed out that a child's conceptual abilities prevent them from recognizing the difference between "11" and "1-1."
Solution 2:
911, the phone number, involves a physical pressing of three keys while the car model can be thought of as shorthand for "nine hundred eleven" and the date is a month (9) and a day (11).
The reason 800 in a phone number is used differently, I think, is that it is just one portion of a longer number. Since 800 was the sole toll free long distance exchange for a long time and was used primarily by businesses, advertising probably played a role as 1-8 hundred- whatever flows better in jingles than 1-8-0-0-whatever. Also, since 1-8 hundred compresses the number of elements being conveyed, it makes it easier to remember (IIRC the psychological concept is called chunking - grouping things together to increase ability to remember).
Solution 3:
The Porsche 911 was originally named the "901" but that had to be changed to "911" because Peugeot had the trademark for cars named (X0Y). My guess is that Porsche was already thinking of the car as the "9" series, and the first model's name of the 9 series was changed to "nine eleven" because calling it the "nine one one" wouldn't make sense to them.
Solution 4:
All phone numbers are actually spelled out as separate digits in English, hence nine-one-one (although this is not necessarily the case in other languages, eg. a phone number of 823 4567 might be easily pronounced as the equivalent of eight twenty-three forty-five sixty-seven in a different language).
Marketing or other numbers like this Porsche model number have no such strict rules, they depend much more on established customs. The Porsche happens to come from Germany and the German reference to the model was Neunelfer (or later, with is popularity, even simply Elfer) all along, because this is the standard way to pronounce such numbers in German.