So..

My ISP provider strongly suggest`s me to enable syn pptpd/l2tpd mode.

But, unfortunately, kamikaze 7.09/brcm-2.4 (installed on my device ASUS WL700-gE) can`t be able to
do this: sync ppp support seems completely cuted from  2.4.34 kernel.

Please, include sync ppp support in next release.

For example, my: /etc/ppp/options.pptp

pty "pptp vpn.corbina.net --nolaunchpppd --loglevel 0 --nobuffer"
remotename corbina
ipparam corbina
file /etc/ppp/options.pptp
noipdefault
nodetach
lcp-echo-failure 10
lcp-echo-interval 20
nomppe
nomppc
sync

Cause next /var/log/messages
Apr 30 02:32:02 server pppd[879]: pppd 2.4.3 started by root, uid 0
Apr 30 02:32:02 server pppd[879]: Couldn't set tty to PPP discipline: Invalid argument
Apr 30 02:32:02 server pptp[882]: anon log[main:pptp.c:267]: The synchronous pptp option is NOT activated
Apr 30 02:32:02 server pptp[884]: anon log[ctrlp_rep:pptp_ctrl.c:251]: Sent control packet type is 1 'Start-Control-Connection-Request'
Apr 30 02:32:02 server pptp[884]: anon log[ctrlp_disp:pptp_ctrl.c:732]: Received Start Control Connection Reply
Apr 30 02:32:02 server pptp[884]: anon log[ctrlp_disp:pptp_ctrl.c:766]: Client connection established.
Apr 30 02:32:03 server pptp[884]: anon log[ctrlp_rep:pptp_ctrl.c:251]: Sent control packet type is 7 'Outgoing-Call-Request'
Apr 30 02:32:03 server pptp[884]: anon log[ctrlp_disp:pptp_ctrl.c:851]: Received Outgoing Call Reply.
Apr 30 02:32:03 server pptp[884]: anon log[ctrlp_disp:pptp_ctrl.c:890]: Outgoing call established (call ID 0, peer's call ID 26339).
Apr 30 02:32:03 server pptp[882]: anon warn[decaps_hdlc:pptp_gre.c:197]: short read (-1): Input/output error
Apr 30 02:32:03 server pptp[882]: anon warn[decaps_hdlc:pptp_gre.c:209]: pppd may have shutdown, see pppd log
Apr 30 02:32:03 server pptp[884]: anon log[callmgr_main:pptp_callmgr.c:230]: Closing connection