Ok, after trying to get it to fail again I finally managed it. This is the syslog: Aug 4 07:48:59 mike-laptop kernel: [69033.385030] usb 2-1: new full speed USB device using uhci_hcd and address 7 Aug 4 07:48:59 mike-laptop kernel: [69033.559814] usb 2-1: configuration #1 chosen from 1 choice Aug 4 07:48:59 mike-laptop kernel: [69033.567797] cdc_acm 2-1:1.0: ttyACM0: USB ACM device Aug 4 07:49:00 mike-laptop nm-system-settings: SCPlugin-Ifupdown: device added (udi: /org/freedesktop/Hal/devices/usb_device_22b8_3002_noserial_if0_serial_unknown_0_3, iface: (null)): iface not found Aug 4 07:49:00 mike-laptop NetworkManager: (ttyACM0): found serial port (udev:GSM hal:GSM) Aug 4 07:49:00 mike-laptop NetworkManager: (ttyACM0): new Modem device (driver: 'cdc_acm') Aug 4 07:49:00 mike-laptop NetworkManager: (ttyACM0): exported as /org/freedesktop/Hal/devices/usb_device_22b8_3002_noserial_if0_serial_unknown_0_3 Aug 4 07:49:05 mike-laptop NetworkManager: (ttyACM0): device state change: 1 -> 2 Aug 4 07:49:05 mike-laptop NetworkManager: (ttyACM0): deactivating device (reason: 2). Aug 4 07:49:05 mike-laptop NetworkManager: nm_system_device_flush_ip4_routes_with_iface: assertion `iface_idx >= 0' failed Aug 4 07:49:05 mike-laptop NetworkManager: nm_system_device_flush_ip4_addresses_with_iface: assertion `iface_idx >= 0' failed Aug 4 07:49:05 mike-laptop NetworkManager: (ttyACM0): device state change: 2 -> 3 Aug 4 07:49:05 mike-laptop NetworkManager: Activation (ttyACM0) starting connection 'Vodafone' Aug 4 07:49:05 mike-laptop NetworkManager: (ttyACM0): device state change: 3 -> 4 Aug 4 07:49:05 mike-laptop NetworkManager: Activation (ttyACM0) Stage 1 of 5 (Device Prepare) scheduled... Aug 4 07:49:05 mike-laptop NetworkManager: Activation (ttyACM0) Stage 1 of 5 (Device Prepare) started... Aug 4 07:49:05 mike-laptop NetworkManager: [1249328945.012171] nm_serial_device_open(): (ttyACM0) opening device... Aug 4 07:49:05 mike-laptop NetworkManager: Activation (ttyACM0) Stage 1 of 5 (Device Prepare) complete. Aug 4 07:49:05 mike-laptop NetworkManager: (ttyACM0): powering up... Aug 4 07:49:05 mike-laptop NetworkManager: Registered on Home network Aug 4 07:49:05 mike-laptop NetworkManager: Associated with network: +COPS: 0,0,"vodafone NZ" Aug 4 07:49:05 mike-laptop NetworkManager: Connected, Woo! Aug 4 07:49:05 mike-laptop NetworkManager: Activation (ttyACM0) Stage 2 of 5 (Device Configure) scheduled... Aug 4 07:49:05 mike-laptop NetworkManager: Activation (ttyACM0) Stage 2 of 5 (Device Configure) starting... Aug 4 07:49:05 mike-laptop NetworkManager: (ttyACM0): device state change: 4 -> 5 Aug 4 07:49:05 mike-laptop NetworkManager: Starting pppd connection Aug 4 07:49:05 mike-laptop NetworkManager: [1249328945.937676] nm_ppp_manager_start(): Command line: /usr/sbin/pppd nodetach lock nodefaultroute user web ttyACM0 noipdefault noauth usepeerdns lcp-echo-failure 0 lcp-echo-interval 0 ipparam /org/freedesktop/NetworkManager/PPP/6 plugin /usr/lib/pppd/2.4.4/nm-pppd-plugin.so Aug 4 07:49:05 mike-laptop NetworkManager: [1249328945.941711] nm_ppp_manager_start(): ppp started with pid 31909 Aug 4 07:49:05 mike-laptop NetworkManager: Activation (ttyACM0) Stage 2 of 5 (Device Configure) complete. Aug 4 07:49:05 mike-laptop pppd[31909]: Plugin /usr/lib/pppd/2.4.4/nm-pppd-plugin.so loaded. Aug 4 07:49:05 mike-laptop pppd[31909]: pppd 2.4.5 started by root, uid 0 Aug 4 07:49:05 mike-laptop pppd[31909]: Using interface ppp0 Aug 4 07:49:05 mike-laptop pppd[31909]: Connect: ppp0 <--> /dev/ttyACM0 Aug 4 07:49:05 mike-laptop pppd[31909]: PAP authentication succeeded Aug 4 07:49:11 mike-laptop pppd[31909]: Cannot determine ethernet address for proxy ARP Aug 4 07:49:11 mike-laptop pppd[31909]: local IP address 124.6.218.90 Aug 4 07:49:11 mike-laptop pppd[31909]: remote IP address 192.168.100.101 Aug 4 07:49:11 mike-laptop pppd[31909]: primary DNS address 202.73.206.16 Aug 4 07:49:11 mike-laptop pppd[31909]: secondary DNS address 202.73.198.16 Aug 4 07:49:20 mike-laptop NetworkManager: pppd_timed_out(): Looks like pppd didn't initialize our dbus module Aug 4 07:49:20 mike-laptop NetworkManager: (ttyACM0): device state change: 5 -> 9 Aug 4 07:49:20 mike-laptop pppd[31909]: Terminating on signal 15 Aug 4 07:49:20 mike-laptop NetworkManager: [1249328961.000824] nm_serial_device_close(): Closing device 'ttyACM0' Aug 4 07:49:20 mike-laptop pppd[31909]: Connect time 0.2 minutes. Aug 4 07:49:20 mike-laptop pppd[31909]: Sent 0 bytes, received 0 bytes. Aug 4 07:49:20 mike-laptop NetworkManager: Marking connection 'Vodafone' invalid. Aug 4 07:49:20 mike-laptop NetworkManager: Activation (ttyACM0) failed. Aug 4 07:49:20 mike-laptop NetworkManager: (ttyACM0): device state change: 9 -> 3 Aug 4 07:49:20 mike-laptop NetworkManager: (ttyACM0): deactivating device (reason: 0). Aug 4 07:49:21 mike-laptop NetworkManager: nm_system_device_flush_ip4_routes_with_iface: assertion `iface_idx >= 0' failed Aug 4 07:49:21 mike-laptop NetworkManager: nm_system_device_flush_ip4_addresses_with_iface: assertion `iface_idx >= 0' failed Aug 4 07:49:21 mike-laptop pppd[31909]: Connection terminated. Aug 4 07:49:21 mike-laptop pppd[31909]: Exit. Aug 4 07:49:23 mike-laptop NetworkManager: [1249328963.002765] ensure_killed(): waiting for ppp pid 31909 to exit Aug 4 07:49:23 mike-laptop NetworkManager: [1249328963.002873] ensure_killed(): ppp pid 31909 cleaned up I tried a second time, same problem. So then I resorted to GNOME PPP, which worked fine: Aug 4 07:52:53 mike-laptop pppd[32261]: pppd 2.4.5 started by mike, uid 1000 Aug 4 07:52:53 mike-laptop pppd[32261]: Using interface ppp0 Aug 4 07:52:53 mike-laptop pppd[32261]: Connect: ppp0 <--> /dev/ttyACM0 Aug 4 07:52:53 mike-laptop pppd[32261]: PAP authentication succeeded Aug 4 07:52:56 mike-laptop pppd[32261]: Cannot determine ethernet address for proxy ARP Aug 4 07:52:56 mike-laptop pppd[32261]: local IP address 124.6.203.94 Aug 4 07:52:56 mike-laptop pppd[32261]: remote IP address 192.168.100.101 Aug 4 07:52:56 mike-laptop pppd[32261]: primary DNS address 202.73.198.16 Aug 4 07:52:56 mike-laptop pppd[32261]: secondary DNS address 202.73.206.16 I am going to have another read through https://bugs.launchpad.net/bugs/371291 and see if this helps.