I would propose also an ifup script checking the ssid and then look to get the automatic checks set to NULL (do not know yet, nothing in phone_control, maybe check with gconf). As just killing modest will not help, it will arise out of the ashes and update again.
cat /etc/network/if-up.d/50_wifiscripts #!/bin/sh essid=$(iwgetid -s) if [ "$essid" == "home" ]; then iwconfig wlan0 txpower 4 echo $essid elif [ "$essid" == "work" ]; then iwconfig wlan0 txpower 6 fi