private char[] getCharSetForNumber(int num) {
        switch(num){
            case 1 : return "abc".toCharArray();
            case 2 : return "def".toCharArray();
            case 3: return "ghi".toCharArray();
            case 4: return "jkl".toCharArray();
            case 5: return "mno".toCharArray();
            case 6: return "pqrs".toCharArray();
            case 8: return "tuv".toCharArray();
            case 9: return "wxyz".toCharArray();
        }
        throw new IllegalArgumentException();
    }
http://stackoverflow.com/questions/2344496/how-can-i-print-out-all-possible-letter-combinations-a-given-phone-number-can-re
src/com/interview/recursion/KeyPadPermutation.java