DHCP over bridge between WiFi and wired

[Barak Pearlmutter <barak@cs.may.ie>]

I have a WAP which serves DHCP requests.
I have a laptop with an 802.11b interface.  The laptop connects
to the WAP and gets its IP address via DHCP.
I have another device (Grandstream BudgeTone-101, a non-wireless SIP
phone) which uses DHCP as it boots.
The laptop has an otherwise-unused wired ethernet interface.
I would like to use the laptop as a bridge, thus allowing the SIP
phone to plug into the laptop while I'm laying in bed.

    $ grep -A9 br0 /etc/network/interfaces

    iface br0 inet dhcp
	    pre-up egrep --silent '^3c59x' /proc/modules || modprobe 3c59x
	    pre-up /etc/init.d/pcmcia start || true
	    pre-up cardctl insert || true
	    pre-up ifconfig eth0 down || true
	    pre-up ifconfig eth1 down || true
	    bridge_ports all
	    bridge_maxwait 5
	    bridge_stp on

The bridge seems to work fine, except that the SIP phone never gets
its IP address.  Ie DHCP does not seem to completely cross the bridge.

Any hints?
--
Barak A. Pearlmutter <barak@cs.may.ie>
 Hamilton Institute, NUI Maynooth, Co. Kildare, Ireland
 http://www-bcl.cs.may.ie/~barak/