Infos :
The kernel enable USBNET : Ethernet over USB, you can show your phone by an connected USB Ethernet adaptor.
This is very good for connect to the Debian, beacause I don't find a file to overlap the keyboard layourt.

If you want ext3 for the Native Debian, for esier acces, make an ext2 in first time and when Debian boot is OK, you can convert.
OR, make an Android kernel with ext3 support !

My kernel is based on OpenMoko Wiki, but I make my initramfs to get an Debian style.
Requires :
Split your SDCARD into 3 primary partitions.
Mine :
- 4 Gb in FAT32 for Android space.
- 4 Gb in ext2 for Android Apps and space for the system.
- 8 Gb in ext2 for Debian Native. (in my 2nd version of the kernel I have ext3 for journalising :-))

In the third partition, debootstrap an Lenny Debian.
You can debootstrap with an Android Debian with mount manualy the third partition in /mnt.
Or,
You can debootstrap the first stage with your home PC and chroot in with the Android ADB to execute the second stage.
Chroot in.
make this commands :
apt-get install udev ssh

edit /etc/network/interfaces

auto usb0
iface usb0 inet static
        address 192.168.0.202
        netmask 255.255.255.0
        network 192.168.0.0
        up route add default gw 192.168.0.200 metric 8
        down route del default gw 192.168.0.200 metric 8

edit /etc/resolv.conf and add "nameserver XXX.XXX.XXX.XXX"

You can set the root password with "passwd".

To connect on the phone by USB Network type all command in your Linux PC :
ifconfig usb0 192.168.0.200 netmask 255.255.255.0 up

This is for Internet Sharing to allow G1 phone contact WWW
sysctl -w net.ipv4.ip_forward=1
iptables -A POSTROUTING -t nat -j MASQUERADE -s 192.168.0.0/24

You can now connect to the phone with ssh 192.168.0.202 !
Don't forget to connect with root on G1 Console and type passwd to set the password !