This tar file (wpa-roaming.tar) contains helpful files to set up WPA roaming

Prereqs:
 * opkg install bash
 * modify /etc/network/interfaces for wpa roaming, e.g.:
iface eth0 inet manual
        wpa-roam /etc/wpa_supplicant/wpa_supplicant.conf
	down wpa_action eth0 down

iface default inet dhcp

iface myhomenet inet static
	address 192.168.123.123
	netmask 255.255.255.0
	gateway 192.168.123.1
	up grep -q 192.168.123.1 /etc/resolv.conf || echo "nameserver 192.168.123.1" >> /etc/resolv.conf
	down sed '/nameserver 192.168.123.1/d' -i /etc/resolv.conf

 * configure your wpa_supplicant.conf and use id_str if necessary, e.g.

#id_str -> myhomenet will be used -> static IP
network={
	ssid="Home Net"
	psk="myverysecretkey"
	id_str="myhomenet"
}

#no id_str -> default will be used -> dhcp
network={
	ssid="Another Net"
	psk="myverysecretkey2"
}

 * I also deactivate conman (exit in init script) but this is probably not necessary

see also:
http://wiki.debian.org/WPA