use WWW::Mechanize qw(); # I hate 4 arguments LWP::UserAgent::credentials
my $uri = 'urn:dslforum-org:service:DeviceConfig:1';
my $action = 'Reboot';
my $m = WWW::Mechanize->new(timeout => 5);
$m->credentials($ENV{FRITZUSER} => $ENV{FRITZPW});
$m->add_header(SoapAction => "$uri#$action");
$m->post(
    "http://$ENV{FRITZIP}:49000/upnp/control/deviceconfig",
    content => <<"XML"
<?xml version='1.0' encoding='utf-8'?>
<s:Envelope
    s:encodingStyle='http://schemas.xmlsoap.org/soap/encoding/'
    xmlns:s='http://schemas.xmlsoap.org/soap/envelope/'
>
    <s:Body>
        <u:$action xmlns:u='$uri'></u:$action>
    </s:Body>
</s:Envelope>
XML
);