En base a lo que se describe en http://www.voip-info.org/wiki/view/SIP-T28

Se puede configurar el directorio telefónico remoto en el telefóno Yealink SIP T28P utilizando Elastix, para esto se debe crear un archivo en la carpeta /var/www/html , llamado por ejemplo, directorio.php con lo siguiente:

<?php
print("\n");
print("\n");
print("Prompt\n");
set_time_limit(5);
system("/usr/sbin/asterisk -rx \"database show AMPUSER\" > /tmp/asterisk_cid-list.txt");
$fd=fopen("/tmp/asterisk_cid-list.txt","r");
while ($line=fgets($fd,1000))
{
if (strpos ($line,"cidname") == true) {
$nome=trim(substr($line,strpos($line,":")+1));
print("\n");
print("");
print($nome);
print("\n");
}
if (strpos ($line,"cidnum") == true) {
$numero=trim(substr($line,strpos($line,":")+1));
print("");
print($numero);
print("\n");
print("\n");
}
}
fclose ($fd);
print("");
?>

Luego en la configuración del teléfono, ir a Contactos -> Agenda telefónica remota e ingresar la dirección http://ip_servidor_voip/directorio.php y listo!

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Based on what is described in http://www.voip-info.org/wiki/view/SIP-T28

You can configure the remote phonebook on a Yealink SIP Phone T28P using Elastix, for this you should create a file in the folder /var/www/html, called for example, directorio.php with the following:

<?php
print("\n");
print("\n");
print("Prompt\n");
set_time_limit(5);
system("/usr/sbin/asterisk -rx \"database show AMPUSER\" > /tmp/asterisk_cid-list.txt");
$fd=fopen("/tmp/asterisk_cid-list.txt","r");
while ($line=fgets($fd,1000))
{
if (strpos ($line,"cidname") == true) {
$nome=trim(substr($line,strpos($line,":")+1));
print("\n");
print("");
print($nome);
print("\n");
}
if (strpos ($line,"cidnum") == true) {
$numero=trim(substr($line,strpos($line,":")+1));
print("");
print($numero);
print("\n");
print("\n");
}
}
fclose ($fd);
print("");
?>

Then in the phone settings, go to Contacts -> Remote phonebook and enter the address http://voip_server_address/directorio.php and try it!