Thank you for the answer, Klaus

I have tried your way(commented my subst and added your rows), so now it looks like this:

failure_route[2] {
if (!t_is_canceled() && t_check_status("486|408")) { 
$avp(alias_seq)=$avp(alias_seq)+1;
xdbg("HERE WE ARE!    $avp(alias_seq)\n");  
revert_uri();
sql_query("main", "select username from subscriber where alias='$tU' and alias_seq='$avp(alias_seq)'", "alias_name"); 
sql_query("main", "select domain from subscriber where alias='$tU' and alias_seq='$avp(alias_seq)'", "alias_domain"); 
if ($dbr(alias_name=>rows) != 0 && $dbr(alias_domain=>rows) != 0) {
subst_uri('/^sip:.*@.*$/sip:$dbr(alias_name=>[0,0])@$dbr(alias_domain=>[0,0])/');
# subst('/^To:.*<sip:.*>/To: <sip:$dbr(alias_name=>[0,0])@$dbr(alias_domain=>[0,0])>\r\n/');     <--COMMENTED OUT THIS ONE
remove_hf("To");                                                                                                           # <--ADDED THIS ONE 
append_hf("To: <sip:$dbr(alias_name=>[0,0])@$dbr(alias_domain=>[0,0])>\r\n");   # <--ADDED THIS ONE
sql_result_free("alias_name");
sql_result_free("alias_domain");
setflag(10);
if (!lookup("location")) {
   switch ($retcode) {
case -1:
case -3:
t_reply("404", "Not Found");
exit;
case -2:
exit;
   }
}
append_branch();
route(5);
}
}
if (is_method("INVITE")) {
unforce_rtp_proxy();
}

}

route[5] {
if (!t_relay()) {
sl_reply_error();
}
exit;
}

So the code now supposed to delete "To: <sip:ncm0000b@domain.com>"
and to append                                          "To: <sip:ncm0000a@domain.com>"

But with ngrep i can see:
To: <sip:ncm0000b@domain.com>.Date: Tue, 08 Jun 2010 09:40:10 GMT.

With timestamp, which seems to me to be unusual.

So maybe it's impossible to rewrite "To" header from failure_route for some reason... (For example according to RFC)

Actually my phones ring, and everything works fine, I am just interested with this behavior of Kamailio.

Thanks again for your reply. 

Sincerely yours,
Kosilov Fedor.


2010/6/8 Klaus Darilion <klaus.mailinglists@pernau.at>
 remove_hf("To");
 append_hf("To: <sip:$dbr(alias_name=>[0,0])@$dbr(alias_domain=>[0,0])>\r\n");