Thanks to the awesome work of Diego Giagio (for writing it) and Paul McEnery (for packaging it for Debian), using your iPhone as a modem under Debian is about 60 seconds work:

1. Install ipheth-dkms (the kernel module side of things) and ipheth-utils (the userspace pairing daemon).
2. watch the postinst build the kernel driver for your current kernel
3. plug your phone in

4. dmesg|grep iPhone should show something like:

   [867025.370421] ipheth 3-2:4.2: Apple iPhone USB Ethernet device attached

   and you’ll find you have a new Ethernet interface

5. enable tethering on the phone (Settings -> General -> Network -> Internet Tethering)
6. now the ethernet interface is running a DHCP server - select it with nm-applet or ifup it or whatever you normally do