(PHP 5 >= 5.1.3)
timezone_name_from_abbr — Returns the timezone name from abbreviation
$abbr
   [, int $gmtOffset = -1
   [, int $isdst = -1
  ]] )
abbr
     Time zone abbreviation.
gmtOffset
     
       Offset from GMT in seconds. Defaults to -1 which means that first found
       time zone corresponding to abbr is returned.
       Otherwise exact offset is searched and only if not found then the first
       time zone with any offset is returned.
      
isdst
     
       Daylight saving time indicator. Defaults to -1, which means that
       whether the time zone has daylight saving or not is not taken into
       consideration when searching. If this is set to 1, then the
       gmtOffset is assumed to be an offset with
       daylight saving in effect; if 0, then gmtOffset
       is assumed to be an offset without daylight saving in effect. If
       abbr doesn't exist then the time zone is
       searched solely by the gmtOffset and
       isdst.
      
   Returns time zone name on success or FALSE on failure.
  
Example #1 A timezone_name_from_abbr() example
<?php
echo timezone_name_from_abbr("CET") . "\n";
echo timezone_name_from_abbr("", 3600, 0) . "\n";
?>
The above example will output something similar to:
Europe/Berlin Europe/Paris