For me, network manager doesn't even seem to detect that a PIN secret is needed:

Nov  3 23:17:50 motin-xps NetworkManager: <info>  Activation (ttyUSB1) starting connection '3' 
Nov  3 23:17:50 motin-xps NetworkManager: <info>  (ttyUSB1): device state change: 3 -> 4 
Nov  3 23:17:50 motin-xps NetworkManager: <info>  Activation (ttyUSB1) Stage 1 of 5 (Device Prepare) scheduled... 
Nov  3 23:17:50 motin-xps NetworkManager: <info>  Activation (ttyUSB1) Stage 1 of 5 (Device Prepare) started... 
Nov  3 23:17:50 motin-xps NetworkManager: <debug> [1225750670.413341] nm_serial_device_open(): (ttyUSB1) opening device... 
Nov  3 23:17:50 motin-xps NetworkManager: <info>  Activation (ttyUSB1) Stage 1 of 5 (Device Prepare) complete. 
Nov  3 23:17:50 motin-xps NetworkManager: <WARN>  init_done(): Modem initialization failed 
Nov  3 23:17:50 motin-xps NetworkManager: <info>  (ttyUSB1): device state change: 4 -> 9 
Nov  3 23:17:50 motin-xps NetworkManager: <debug> [1225750670.568802] nm_serial_device_close(): Closing device 'ttyUSB1' 
Nov  3 23:17:50 motin-xps NetworkManager: <info>  Marking connection '3' invalid. 
Nov  3 23:17:50 motin-xps NetworkManager: <info>  Activation (ttyUSB1) failed. 
Nov  3 23:17:50 motin-xps NetworkManager: <info>  (ttyUSB1): device state change: 9 -> 3 
Nov  3 23:17:50 motin-xps NetworkManager: <info>  (ttyUSB1): deactivating device (reason: 0). 
Nov  3 23:17:50 motin-xps NetworkManager: nm_system_device_flush_ip4_routes_with_iface: assertion `iface_idx >= 0' failed
Nov  3 23:17:50 motin-xps NetworkManager: nm_system_device_flush_ip4_addresses_with_iface: assertion `iface_idx >= 0' failed

After having started UMTSMon, which correctly asks and receives the PIN code, or running the AT+CPIN command against /dev/ttyUSB0, the following log is given after a success connection has been made:

Nov  3 23:20:33 motin-xps NetworkManager: <info>  Activation (ttyUSB1) starting connection '3' 
Nov  3 23:20:33 motin-xps NetworkManager: <info>  (ttyUSB1): device state change: 3 -> 4 
Nov  3 23:20:33 motin-xps NetworkManager: <info>  Activation (ttyUSB1) Stage 1 of 5 (Device Prepare) scheduled... 
Nov  3 23:20:33 motin-xps NetworkManager: <info>  Activation (ttyUSB1) Stage 1 of 5 (Device Prepare) started... 
Nov  3 23:20:33 motin-xps NetworkManager: <debug> [1225750833.637118] nm_serial_device_open(): (ttyUSB1) opening device... 
Nov  3 23:20:33 motin-xps NetworkManager: <info>  Activation (ttyUSB1) Stage 1 of 5 (Device Prepare) complete. 
Nov  3 23:20:33 motin-xps NetworkManager: <info>  (ttyUSB1): powering up... 
Nov  3 23:20:33 motin-xps NetworkManager: <info>  Registered on Home network 
Nov  3 23:20:34 motin-xps NetworkManager: <info>  Associated with network: +COPS: 1,0,"3",2 
Nov  3 23:20:34 motin-xps NetworkManager: <info>  Connected, Woo! 
Nov  3 23:20:34 motin-xps NetworkManager: <info>  Activation (ttyUSB1) Stage 2 of 5 (Device Configure) scheduled... 
Nov  3 23:20:34 motin-xps NetworkManager: <info>  Activation (ttyUSB1) Stage 2 of 5 (Device Configure) starting... 
Nov  3 23:20:34 motin-xps NetworkManager: <info>  (ttyUSB1): device state change: 4 -> 5 
Nov  3 23:20:34 motin-xps NetworkManager: <info>  Starting pppd connection 
Nov  3 23:20:34 motin-xps NetworkManager: <debug> [1225750834.417329] nm_ppp_manager_start(): Command line: /usr/sbin/pppd nodetach lock ttyUSB1 noipdefault usepeerdns ipparam /org/freedesktop/NetworkManager/PPP/10 plugin /usr/lib/pppd/2.4.4/nm-pppd-plugin.so 
Nov  3 23:20:34 motin-xps pppd[27991]: Plugin /usr/lib/pppd/2.4.4/nm-pppd-plugin.so loaded.
Nov  3 23:20:34 motin-xps pppd[27991]: pppd 2.4.4 started by root, uid 0
Nov  3 23:20:34 motin-xps NetworkManager: <debug> [1225750834.423837] nm_ppp_manager_start(): ppp started with pid 27991 
Nov  3 23:20:34 motin-xps NetworkManager: <info>  Activation (ttyUSB1) Stage 2 of 5 (Device Configure) complete. 
Nov  3 23:20:34 motin-xps pppd[27991]: Using interface ppp0
Nov  3 23:20:34 motin-xps pppd[27991]: Connect: ppp0 <--> /dev/ttyUSB1
Nov  3 23:20:34 motin-xps NetworkManager: <info>  (ttyUSB1): device state change: 5 -> 6 
Nov  3 23:20:34 motin-xps pppd[27991]: CHAP authentication succeeded
Nov  3 23:20:34 motin-xps pppd[27991]: CHAP authentication succeeded
Nov  3 23:20:34 motin-xps NetworkManager: <info>  (ttyUSB1): device state change: 6 -> 7 
Nov  3 23:20:38 motin-xps pppd[27991]: Could not determine remote IP address: defaulting to 10.64.64.64
Nov  3 23:20:38 motin-xps pppd[27991]: Cannot determine ethernet address for proxy ARP
Nov  3 23:20:38 motin-xps pppd[27991]: local  IP address 94.191.153.246
Nov  3 23:20:38 motin-xps pppd[27991]: remote IP address 10.64.64.64
Nov  3 23:20:38 motin-xps pppd[27991]: primary   DNS address 80.251.192.244
Nov  3 23:20:38 motin-xps pppd[27991]: secondary DNS address 80.251.192.245
Nov  3 23:20:38 motin-xps NetworkManager: <info>  PPP manager(IP Config Get) reply received. 
Nov  3 23:20:38 motin-xps NetworkManager: <info>  Activation (ttyUSB1) Stage 4 of 5 (IP Configure Get) scheduled... 
Nov  3 23:20:38 motin-xps NetworkManager: <info>  Activation (ttyUSB1) Stage 4 of 5 (IP Configure Get) started... 
Nov  3 23:20:38 motin-xps NetworkManager: <info>  Activation (ttyUSB1) Stage 5 of 5 (IP Configure Commit) scheduled... 
Nov  3 23:20:38 motin-xps NetworkManager: <info>  Activation (ttyUSB1) Stage 4 of 5 (IP Configure Get) complete. 
Nov  3 23:20:38 motin-xps NetworkManager: <info>  Activation (ttyUSB1) Stage 5 of 5 (IP Configure Commit) started... 
Nov  3 23:20:39 motin-xps NetworkManager: <info>  (ttyUSB1): device state change: 7 -> 8 
Nov  3 23:20:39 motin-xps NetworkManager: <info>  Clearing nscd hosts cache. 
Nov  3 23:20:39 motin-xps NetworkManager: <info>  Policy set '3' (ppp0) as default for routing and DNS. 
Nov  3 23:20:39 motin-xps NetworkManager: <info>  Activation (ttyUSB1) successful, device activated. 
Nov  3 23:20:39 motin-xps NetworkManager: <info>  Activation (ttyUSB1) Stage 5 of 5 (IP Configure Commit) complete. 
Nov  3 23:20:40 motin-xps nm-dispatcher.action: Script '/etc/NetworkManager/dispatcher.d/01ifupdown' exited with error status 1.
Nov  3 23:20:40 motin-xps ntpd[16682]: ntpd exiting on signal 15
Nov  3 23:20:41 motin-xps ntpdate[28401]: adjust time server 192.36.143.150 offset 0.002729 sec
Nov  3 23:20:41 motin-xps ntpd[28444]: ntpd 4.2.4p4@1.1520-o Wed Aug 20 17:03:52 UTC 2008 (1)
Nov  3 23:20:41 motin-xps ntpd[28445]: precision = 2.000 usec
Nov  3 23:20:41 motin-xps ntpd[28445]: Listening on interface #0 wildcard, 0.0.0.0#123 Disabled
Nov  3 23:20:41 motin-xps ntpd[28445]: Listening on interface #1 lo, 127.0.0.1#123 Enabled
Nov  3 23:20:41 motin-xps ntpd[28445]: Listening on interface #2 ppp0, 94.191.153.246#123 Enabled
Nov  3 23:20:41 motin-xps ntpd[28445]: kernel time sync status 0040
Nov  3 23:20:41 motin-xps ntpd[28445]: frequency initialized -14.059 PPM from /var/lib/ntp/ntp.drift
Nov  3 23:20:41 motin-xps ntpd[28445]: getaddrinfo: "::1" invalid host address, ignored