For telephone numbers, product codes etc. the first method would be my preference, but the second could also be used. But definitely not 3. We would only use the whole number way of expression for something countable. Sorry, don't know what 'language-directive' means.

There aren't any formal rules I know of. In the U.S. it tends to depend on the the length and kind of the number, and what other numbers in the same series are like. There can be customs within an industry. Method number 3 would not be used unless it is a round number. The Motorola 68000 processor was called the "sixty-eight thousand." The Airbus A300 would read as "A three hundred." Spelling it out digit by digit would only be used if you were placing an order over the telephone or talking to someone who was unfamiliar with the technology or product line. For a three-digit number, it is very common to use a 1-2 pattern. Thus, the Boeing 767 would be "the Boeing seven sixty-seven." The Airbus A380, "A three eighty." For a four-digit number, it is very common to use a 2-2 pattern. The IBM 7094 was the "IBM seventy ninety-four." In the U.S. the digit zero is usually read as "oh," like the letter O. This influenced the way numbers are read. The Boeing 707 was "the seven-oh-seven." Occasionally you will get a number written with leading zeroes, and these are read as "oh." The Zebco Omega Z03 Spincast Reel would be read as "Z oh three." For your two examples, I'd read the first as "H G twelve-eighty." The second is awkward. I believe I'd read it as "H G thirty-four five-twenty-one." A 2 + 3 pattern.