$text = "via delle salsiccie, 77/m - 00156 riom (in)";
echo $text."

";

$text = eregi_replace("([0-9]{1,3})/([a-z]{1})\040", "\\1/".strtoupper("\\2a")."\040", $text);
echo $text;
tu prima applichi la toupper e poi la regex !

eregi("([0-9]{1,3})/([a-z])\040", $text, $regs);
echo $regs[1], strtoupper($regs[2]), "\040",