Kubuntu 9.04
Воспользовавшись мануалом
http://silverghost.org.ua/2009/07/27/mts-konnekt-c-motech-cnu-680-v-ubuntu-9-04/ настроил монтирование модема и подключения к интернету.
Проблема всегда одна и та же! Через некоторое время модем постоянно "отваливается" (через 10-15 секунд, бывает и по 30 минут) и заново переподключается (но чаще передергиваю модем). При этом соединение приходится востанавливать.
Пробовал варианты: kppp, nm, просто pppd - исход один и тот же. Читал о косяках nm и удалил его полностью. Не помогло

Странность еще в том, что модем отваливается и когда нет подключения. Включил комп... подключаю интернет и в логах следующие строки:
2010-09-09 11:13:05 mikolasan kernel [ 686.168015] usb 2-1: reset full speed USB device using ohci_hcd and address 4
2010-09-09 11:13:05 mikolasan kernel [ 686.395073] cdc_acm 2-1:1.0: ttyACM0: USB ACM device
2010-09-09 11:14:06 mikolasan kernel [ 747.164015] usb 2-1: reset full speed USB device using ohci_hcd and address 4
2010-09-09 11:14:06 mikolasan kernel [ 747.391071] cdc_acm 2-1:1.0: ttyACM0: USB ACM device
2010-09-09 11:15:07 mikolasan kernel [ 808.164015] usb 2-1: reset full speed USB device using ohci_hcd and address 4
2010-09-09 11:15:07 mikolasan kernel [ 808.391074] cdc_acm 2-1:1.0: ttyACM0: USB ACM device
2010-09-09 11:16:08 mikolasan kernel [ 869.165014] usb 2-1: reset full speed USB device using ohci_hcd and address 4
2010-09-09 11:16:08 mikolasan kernel [ 869.391073] cdc_acm 2-1:1.0: ttyACM0: USB ACM device
2010-09-09 11:16:27 mikolasan pppd[4465] pppd 2.4.5 started by root, uid 0
2010-09-09 11:16:27 mikolasan pppd[4465] Using interface ppp0
2010-09-09 11:16:27 mikolasan pppd[4465] Connect: ppp0 <--> /dev/ttyACM0
2010-09-09 11:16:30 mikolasan pppd[4465] CHAP authentication succeeded
2010-09-09 11:16:30 mikolasan pppd[4465] CHAP authentication succeeded
2010-09-09 11:16:30 mikolasan vmnetBridge RTM_NEWROUTE: index:11
2010-09-09 11:16:30 mikolasan pppd[4465] Cannot determine ethernet address for proxy ARP
2010-09-09 11:16:30 mikolasan pppd[4465] local IP address 77.52.93.26
2010-09-09 11:16:30 mikolasan pppd[4465] remote IP address 80.255.77.39
2010-09-09 11:17:09 mikolasan pppd[4465] Hangup (SIGHUP)
2010-09-09 11:17:09 mikolasan pppd[4465] Modem hangup
2010-09-09 11:17:09 mikolasan pppd[4465] Connect time 0.7 minutes.
2010-09-09 11:17:09 mikolasan pppd[4465] Sent 83424 bytes, received 195294 bytes.
2010-09-09 11:17:09 mikolasan pppd[4465] Connection terminated.
2010-09-09 11:17:09 mikolasan pppd[4465] Exit.
2010-09-09 11:17:09 mikolasan kernel [ 930.184015] usb 2-1: reset full speed USB device using ohci_hcd and address 4
2010-09-09 11:17:09 mikolasan kernel [ 930.413078] cdc_acm 2-1:1.0: ttyACM0: USB ACM device
2010-09-09 11:17:19 mikolasan pppd[4600] pppd 2.4.5 started by root, uid 0
2010-09-09 11:17:19 mikolasan pppd[4600] Using interface ppp0
2010-09-09 11:17:19 mikolasan pppd[4600] Connect: ppp0 <--> /dev/ttyACM0
2010-09-09 11:17:22 mikolasan pppd[4600] CHAP authentication succeeded
2010-09-09 11:17:22 mikolasan pppd[4600] CHAP authentication succeeded
2010-09-09 11:17:22 mikolasan pppd[4600] Cannot determine ethernet address for proxy ARP
2010-09-09 11:17:22 mikolasan pppd[4600] local IP address 77.52.93.26
2010-09-09 11:17:22 mikolasan pppd[4600] remote IP address 80.255.77.39
2010-09-09 11:17:22 mikolasan vmnetBridge RTM_NEWROUTE: index:12
2010-09-09 11:18:10 mikolasan pppd[4600] Hangup (SIGHUP)
2010-09-09 11:18:10 mikolasan pppd[4600] Modem hangup
2010-09-09 11:18:10 mikolasan pppd[4600] Connect time 0.8 minutes.
2010-09-09 11:18:10 mikolasan pppd[4600] Sent 53725 bytes, received 302869 bytes.
2010-09-09 11:18:10 mikolasan pppd[4600] Connection terminated.
2010-09-09 11:18:10 mikolasan pppd[4600] Exit.
2010-09-09 11:18:10 mikolasan kernel [ 991.176023] usb 2-1: reset full speed USB device using ohci_hcd and address 4
2010-09-09 11:18:10 mikolasan kernel [ 991.407079] cdc_acm 2-1:1.0: ttyACM0: USB ACM device
2010-09-09 11:18:17 mikolasan pppd[4642] pppd 2.4.5 started by root, uid 0
2010-09-09 11:18:17 mikolasan pppd[4642] Using interface ppp0
2010-09-09 11:18:17 mikolasan pppd[4642] Connect: ppp0 <--> /dev/ttyACM0
2010-09-09 11:18:21 mikolasan pppd[4642] CHAP authentication succeeded
2010-09-09 11:18:21 mikolasan pppd[4642] CHAP authentication succeeded
2010-09-09 11:18:21 mikolasan pppd[4642] Cannot determine ethernet address for proxy ARP
2010-09-09 11:18:21 mikolasan pppd[4642] local IP address 77.52.93.26
2010-09-09 11:18:21 mikolasan pppd[4642] remote IP address 80.255.77.39
2010-09-09 11:18:21 mikolasan vmnetBridge RTM_NEWROUTE: index:13
2010-09-09 11:19:11 mikolasan pppd[4642] Hangup (SIGHUP)
2010-09-09 11:19:11 mikolasan pppd[4642] Modem hangup
2010-09-09 11:19:11 mikolasan pppd[4642] Connect time 0.9 minutes.
2010-09-09 11:19:11 mikolasan pppd[4642] Sent 2192 bytes, received 2323 bytes.
2010-09-09 11:19:11 mikolasan pppd[4642] Connection terminated.
2010-09-09 11:19:11 mikolasan pppd[4642] Exit.
Может еще что-то выложить нужно?