Undefined index php error on top of the page

Question

I am receving this error on top of the page: Notice: Undefined index: Telephone in /home/public_html/themes/theme/item.php

And below is my code:

Anyone please know how to fix this?? much appreciated! thanks

<?php
if(osc_item_user_id() <> 0) {
  $item_user = User::newInstance()->findByPrimaryKey(osc_item_user_id());
}

$item_meta_data = array();
$mobile_found = true;
while(osc_has_item_meta())
{ 
    $key = osc_item_meta_name();
    $value = osc_item_meta_value();

    $item_meta_data[$key] = $value;
}

$mobile = $item_meta_data['Telephone'];
if($mobile == '') { $mobile_found = false;}

unset($item_meta_data['Telephone']);

if($item_extra['i_sold'] == 1) {
$mobile_found = false;
$mobile = '';
}
?>