For ALPHA/VANITY numbers:
Letters are converted to their numeric representation on a telephone
keypad. The keypad used here is the one defined in ITU Recommendation
E.161. This is only done if there are 3 or more letters in the number,
to lessen the risk that such letters are typos.
For other numbers:
Wide-ascii digits are converted to normal ASCII (European) digits.
Arabic-Indic numerals are converted to European numerals.
Spurious alpha characters are stripped.