You can preserve keys and unshift an array with numerical indexes in a really simple way if you'll do the following:

<?php
$someArray=array(224=>'someword1', 228=>'someword2', 102=>'someword3', 544=>'someword3',95=>'someword4');

$someArray=array(100=>'Test Element 1 ',255=>'Test Element 2')+$someArray;
?>

now the array looks as follows:

array(
100=>'Test Element 1 ',
255=>'Test Element 2'
224=>'someword1',
228=>'someword2',
102=>'someword3',
544=>'someword3',
95=>'someword4'
);

array_merge() will also reindex (see array_merge() manual entry), but the '+' operator won't, so...

<?php
$arrayone=array("newkey"=>"newvalue") + $arrayone;
?>

does the job.

Sahn's example almost works but has a small error. Try it like this if you need to prepend something to the array without the keys being reindexed and/or need to prepend a key value pair, you can use this short function: 

<?php 
function array_unshift_assoc(&$arr, $key, $val) 
{ 
    $arr = array_reverse($arr, true); 
    $arr[$key] = $val; 
    return = array_reverse($arr, true); 
} 
?>

Anonymous' associative version wasn't working for me, but it did with this small tweak:

function array_unshift_assoc(&$arr, $key, $val) 
{ 
    $arr = array_reverse($arr, true); 
    $arr[$key] = $val; 
    $arr = array_reverse($arr, true); 
    return $arr;
}

even simpler unshifting of a reference !
<?php
/**
 * @return int
 * @param $array array
 * @param $value mixed
 * @desc Prepend a reference to an element to the beginning of an array. Renumbers numeric keys, so $value is always inserted to $array[0]
 */
function array_unshift_ref(&$array, &$value)
{
   $return = array_unshift($array,'');
   $array[0] =& $value;
   return $return;
}
?>

This becomes a nice little problem if you index your arrays out of order (while manually sorting).  For example:

<?php
$recordMonths[3] = '8/%/2006';
$recordMonths[4] = '7/%/2004';
$recordMonths[0] = '3/%/2007';
$recordMonths[1] = '2/%/2007';
$recordMonths[5] = '12/%/2000';
$recordMonths[6] = '11/%/2000';
$recordMonths[7] = '10/%/2000';
$recordMonths[2] = '1/%/2007';

for($i = 0; $i < count($recordMonths); $i++)
{
    $singleMonth = $recordMonths[$i];
    echo "singleMonth: $singleMonth <br />";
}
array_unshift($recordMonths,'%');
for($i = 0; $i < count($recordMonths); $i++)
{
    $singleMonth = $recordMonths[$i];
    echo "singleMonth: $singleMonth <br />";
}
?>

Produces:

singleMonth: 3/%/2007
singleMonth: 2/%/2007
singleMonth: 1/%/2007
singleMonth: 8/%/2006
singleMonth: 7/%/2004
singleMonth: 12/%/2000
singleMonth: 11/%/2000
singleMonth: 10/%/2000
singleMonth: %
singleMonth: 8/%/2006
singleMonth: 7/%/2004
singleMonth: 3/%/2007
singleMonth: 2/%/2007
singleMonth: 12/%/2000
singleMonth: 11/%/2000
singleMonth: 10/%/2000
singleMonth: 1/%/2007 

It reindexes them based on the order they were created.  It seems like if an array has all numeric indexes, then it should reindex them based on the order of their index.  Just my opinion...

Actually this problem with the keys getting reindexed only happens when the keys are numerical:

<?php

$a = array("f"=>"five", "s" =>"six", "t" =>
        "twenty");

print_r($a);
echo "\n";
foreach($a as $key=>$val)
{
    echo "k: $key v: $val \n";
}

array_unshift($a, "zero");
print_r($a);
echo "\n";
foreach($a as $key=>$val)
{
    echo "k: $key v: $val \n";
}
?>

Array
(
    [f] => five
    [s] => six
    [t] => twenty
)

k: f v: five
k: s v: six
k: t v: twenty
Array
(
    [0] => zero
    [f] => five
    [s] => six
    [t] => twenty
)

k: 0 v: zero
k: f v: five
k: s v: six
k: t v: twenty

This function helps if you want to prepend a key and value pair to the beginning of an array:

function array_kunshift(array $array, string|int $key, mixed $value): array {
        return array_merge([$key => $value], $array);
    }

Another way to tack something to the beginning of an array is with array_merge().

$plans = array('AARP'=>'Senior', 'AAA'=>'Automobile Club');

$plans = array_merge(array("BAR"=>"Best Available Rate"),  $plans);

If you need to change the name of a key without changing its position in the array this function may be useful.

<?php
function array_key_change($Old, $New, $In, $NewVal=NULL) {
        $Temp = array();
        while(isset($Temp[$Old]) == false) {
                list($k, $v) = each($In);
                $Temp[$k] = $v;
                unset($In[$k]);
        }
        if($NewVal == NULL) {
                $NewVal = $Temp[$Old];
        }
        unset($Temp[$Old]);
        $Temp = array_reverse($Temp);
        $In = array_merge(array($New=>$NewVal), $In);
        while(list($k,$v) = each($Temp)) {
                $In = array_merge(array($k=>$v), $In);
        }
        return($In);
}
?>

If you need to prepend something to the array without the keys being reindexed and/or need to prepend a key value pair, you can use this short function:

<?php
function array_unshift_assoc(&$arr, $key, $val)
{
    $arr = array_reverse($arr, true);
    $arr[$key] = $val;
    $arr = array_reverse($arr, true);
    return count($arr);
}
?>

I had a need tonight to convert a numeric array from 1-based to 0-based, and found that the following worked just fine due to the "side effect" of renumbering:

<?php
   array_unshift( $myArray, array_shift( $myArray ));
?>