Now I solved my problem with 3G->VPN->WiFi by selecting “wan” in Interfaces->VPN_CLIENT->Firewall Settings (screenshot setup_2_8.png).

I agree that use switch to turn on/off OpenVPN is a very good idea.

/etc/rc.button/BTN_1:
if [ “${ACTION}” = “pressed” ]; then
uci set glconfig.openvpn.enable=‘1’
uci commit glconfig
/etc/init.d/startvpn restart
/usr/bin/setvpnfirewall –-force
/etc/init.d/firewall reload
elif [ “${ACTION}” = “released” ]; then
uci set glconfig.openvpn.enable=‘0’
uci commit glconfig
/etc/init.d/startvpn stop
/usr/bin/setvpnfirewall –-disable
/etc/init.d/firewall reload
fi

I see that vpn successfully establishes a connection, but the internet stops working.
I think the problem again in the firewall settings or incorrect routing.
Is it even possible to configure VPN on/off for the “3G->VPN->WiFi” using such a simple script?