Comment 2 for bug 578251

The OS will not recognise any phone hardware after one disconnect - the problem isn't limited to modem connectivity. Rebooting clears this.

From /var/log/messages, during an un-requested disconnect:

Aug 21 19:03:25 r50e kernel: [20603.320176] usb 1-4: new high speed USB device using ehci_hcd and address 4
Aug 21 19:03:25 r50e kernel: [20603.453467] usb 1-4: configuration #1 chosen from 1 choice
Aug 21 19:03:25 r50e kernel: [20603.455735] cdc_acm 1-4:1.1: ttyACM0: USB ACM device
Aug 21 19:03:25 r50e kernel: [20603.457741] usb 1-4: bad CDC descriptors
Aug 21 19:03:25 r50e kernel: [20603.457850] usb 1-4: bad CDC descriptors
Aug 21 19:03:25 r50e kernel: [20603.459353] cdc_phonet: probe of 1-4:1.10 failed with error -22
Aug 21 19:03:28 r50e pppd[4096]: Plugin /usr/lib/pppd/2.4.4/nm-pppd-plugin.so loaded.
Aug 21 19:03:28 r50e pppd[4096]: pppd 2.4.5 started by root, uid 0
Aug 21 19:03:28 r50e pppd[4096]: Using interface ppp0
Aug 21 19:03:28 r50e pppd[4096]: Connect: ppp0 <--> /dev/ttyACM0
Aug 21 19:03:28 r50e pppd[4096]: PAP authentication succeeded
Aug 21 19:03:30 r50e pppd[4096]: local IP address 10.91.59.200
Aug 21 19:03:30 r50e pppd[4096]: remote IP address 10.6.6.6
Aug 21 19:03:30 r50e pppd[4096]: primary DNS address 82.132.254.2
Aug 21 19:03:30 r50e pppd[4096]: secondary DNS address 82.132.254.3
Aug 21 19:04:49 r50e pppd[4096]: Modem hangup
Aug 21 19:04:49 r50e pppd[4096]: Connect time 1.4 minutes.
Aug 21 19:04:49 r50e pppd[4096]: Sent 216233 bytes, received 520210 bytes.
Aug 21 19:04:49 r50e pppd[4096]: Connection terminated.
Aug 21 19:04:49 r50e kernel: [20687.252073] usb 1-4: reset high speed USB device using ehci_hcd and address 4
Aug 21 19:04:49 r50e kernel: [20687.385230] cdc_acm 1-4:1.1: ttyACM0: USB ACM device
Aug 21 19:04:50 r50e pppd[4096]: Terminating on signal 15
Aug 21 19:04:50 r50e pppd[4096]: Exit.
Aug 21 19:05:15 r50e kernel: [20713.618866] usb 1-4: USB disconnect, address 4
Aug 21 19:05:20 r50e kernel: [20718.096197] usb 1-4: new high speed USB device using ehci_hcd and address 5
Aug 21 19:05:20 r50e kernel: [20718.229538] usb 1-4: configuration #1 chosen from 1 choice
Aug 21 19:05:20 r50e kernel: [20718.231816] cdc_acm 1-4:1.1: ttyACM0: USB ACM device
Aug 21 19:05:20 r50e kernel: [20718.233804] usb 1-4: bad CDC descriptors
Aug 21 19:05:20 r50e kernel: [20718.240386] usb 1-4: bad CDC descriptors
Aug 21 19:05:20 r50e kernel: [20718.242974] cdc_phonet: probe of 1-4:1.10 failed with error -22
Aug 21 19:05:47 r50e kernel: [20745.640806] usb 1-4: USB disconnect, address 5