realPhoneNumbers.js

function realPhoneNumber(number){
    if(/^[0-9\s]+$/gi.test(number)){
        return number.replace(/\s+/gi, ""); // no need on a plain number.
    }

    var lookupHash = {
        "a": 2, "b": 2, "c": 2,
        "d": 3, "e": 3, "f": 3,
        "g": 4, "h": 4, "i": 4,
        "j": 5, "k": 5, "l": 5,
        "m": 6, "n": 6, "o": 6,
        "p": 7, "q": 7, "r": 7, "s": 7,
        "t": 8, "u": 8, "v": 8,
        "w": 9, "x": 9, "y": 9, "z": 9
    },
    realNumber = "",
    chars = number.split(""), 
    char, _char;

    while(chars.length && (char=chars.shift())){
        if(char.match(/\s/g)){
            continue;
        }

        _char = parseInt(char, 10);

        if(_char >= 0 && _char < 10){
            realNumber += _char;
        } else {
            realNumber += lookupHash[char.toLowerCase()];
        }
    }
    return realNumber;
}

// Usage:

realPhoneNumber("1800 GET WEBB");
realPhoneNumber("13 11 16");