wvdial diagnostic

[PlanB]

I seem to be 90% of the way to getting an internet connection with wvdial & a USB modem. I've read all the stuff about mode switching & limited power on the USB ports, got that sorted I think. My problem is wvdial hangs at the very last step
--> local IP address 10.181.214.101
--> pppd: ��[06][01]
--> remote IP address 10.64.64.64
--> pppd: ��[06][01]
--> primary DNS address 10.4.81.105
--> pppd: ��[06][01]
--> secondary DNS address 10.4.182.22
--> pppd: ��[06][01]

I'm left with a flashing cursor but I don't get a bash prompt so I think the ppp has hung? If I use ctrlc to terminate dmesg shows
[ 7.068631] usb 1-1.4: new full-speed USB device number 6 using dwc_otg
[ 7.192649] usb 1-1.4: New USB device found, idVendor=12d1, idProduct=1446
[ 7.200690] usb 1-1.4: New USB device strings: Mfr=1, Product=2, SerialNumber=3
[ 7.208238] usb 1-1.4: Product: USB MMC Storage
[ 7.215586] usb 1-1.4: Manufacturer: Qualcomm, Incorporated
[ 7.222511] usb 1-1.4: SerialNumber: \xffffffc3\xffffffbf\xffffffbf\xffffffc3\xffffffbf\xffffffbf\xffffffc3\xffffffbf\xffffffbf\xffffffc3\xffffffbf\xffffffbf\xffffffc3\xffffffbf\xffffffbf\xffffffc3\xffffffbf\xffffffbf\xffffffc3\xffffffbf\xffffffbf\xffffffc3\xffffffbf\xffffffbf\xffffffc3\xffffffbf\xffffffbf\xffffffc3\xffffffbf\xffffffbf\xffffffc3\xffffffbf\xffffffbf\xffffffc3\xffffffbf\xffffffbf
[ 7.232076] usb-storage 1-1.4:1.0: USB Mass Storage device detected
[ 7.239101] scsi host0: usb-storage 1-1.4:1.0
[ 7.312833] usbcore: registered new interface driver uas
[ 8.109128] usb 1-1.4: USB disconnect, device number 6
[ 9.368673] usb 1-1.4: new full-speed USB device number 7 using dwc_otg
[ 9.494975] usb 1-1.4: New USB device found, idVendor=12d1, idProduct=1001
[ 9.501926] usb 1-1.4: New USB device strings: Mfr=1, Product=2, SerialNumber=0
[ 9.509049] usb 1-1.4: Product: Qualcomm CDMA Technologies MSM
[ 9.515599] usb 1-1.4: Manufacturer: Qualcomm, Incorporated
[ 9.527080] usb-storage 1-1.4:1.0: USB Mass Storage device detected
[ 9.537410] usb-storage 1-1.4:1.1: USB Mass Storage device detected
[ 9.547101] usb-storage 1-1.4:1.2: USB Mass Storage device detected
[ 9.555846] usb-storage 1-1.4:1.3: USB Mass Storage device detected
[ 9.565159] scsi host4: usb-storage 1-1.4:1.3
[ 9.607434] usbcore: registered new interface driver usbserial
[ 9.607638] usbcore: registered new interface driver usbserial_generic
[ 9.610110] usbserial: USB Serial support registered for generic
[ 9.627549] usbcore: registered new interface driver option
[ 9.627753] usbserial: USB Serial support registered for GSM modem (1-port)
[ 9.628729] option 1-1.4:1.0: GSM modem (1-port) converter detected
[ 9.633048] usb 1-1.4: GSM modem (1-port) converter now attached to ttyUSB0
[ 9.633263] option 1-1.4:1.1: GSM modem (1-port) converter detected
[ 9.633994] usb 1-1.4: GSM modem (1-port) converter now attached to ttyUSB1
[ 9.634147] option 1-1.4:1.2: GSM modem (1-port) converter detected
[ 9.634957] usb 1-1.4: GSM modem (1-port) converter now attached to ttyUSB2
[ 10.573682] scsi 4:0:0:0: Direct-Access WCDMA MMC Storage 2.31 PQ: 0 ANSI: 2
[ 10.592801] sd 4:0:0:0: [sda] Attached SCSI removable disk
[ 10.612227] sd 4:0:0:0: Attached scsi generic sg0 type 0

Can anyone suggest a diagnostic I can run to find out what's gone wrong?