If you just want something simple:

'$' . number_format($money, 2);

number_format()

This is a US phone formatter that works on more versions of numbers than any of the current answers.

$numbers = explode("\n", '(111) 222-3333
((111) 222-3333
1112223333
111 222-3333
111-222-3333
(111)2223333
+11234567890
    1-8002353551
    123-456-7890   -Hello!
+1 - 1234567890 
');


foreach($numbers as $number)
{
    print preg_replace('~.*(\d{3})[^\d]{0,7}(\d{3})[^\d]{0,7}(\d{4}).*~', '(2-number). "\n";
}

And here is a breakdown of the regex:

Cell: +1 999-(555 0001)

.*          zero or more of anything "Cell: +1 "
(\d{3})     three digits "999"
[^\d]{0,7}  zero or up to 7 of something not a digit "-("
(\d{3})     three digits "555"
[^\d]{0,7}  zero or up to 7 of something not a digit " "
(\d{4})     four digits "0001"
.*          zero or more of anything ")"

Updated: March 11, 2015 to use {0,7} instead of {,7}

From the PHP Manual page on number_format:

string number_format ( float $number , int $decimals = 0 , string $dec_point = '.' , string $thousands_sep = ',' )

If you want numbers like 123456 be formatted as 1234,45, use:

echo number_format($number / 100, 2, ",", "");

If you need a dot as thousands separator (1.234,56):

echo number_format($number / 100, 2, ",", ".");

The zeros are automatically removed by PHP when converting the string to a number.