Thank's for the tip. FYI, I've setup my openvpn network scripts to do this automatically for me. In my case, I only have one VPN connection, and only one SIP server I ever wish to talk to; as such, this may not be applicable to more complex setups.

/etc/network/if-up.d/openvpn:


#!/bin/sh

OPENVPN=/etc/init.d/openvpn

if [ ! -x $OPENVPN ]; then
exit 0
fi

if [ -n "$ICD_CONNECTION_ID" ]; then
$OPENVPN restart $IF_OPENVPN
sleep 5
VPN_INT="tun0"
VPN_IP=`ifconfig $VPN_INT 2> /dev/null | sed -n 's/.*inet[adr: ]*\([0-9]*\.[0-9]*\.[0-9]*\.[0-9]*\).*/\1/p'`
mc-account set sip0 string:local-ip-address=$VPN_IP
fi


I'm using the /etc/network/if-down.d/openvpn script from http://www.internettablettalk.com/fo...ad.php?t=18434

NOTE: I'm using "restart" instead of "start" to avoid problems caused by two openvpn instances running (one started at boot, one started when the wlan interface comes up)