Franklin U772 (U700 series) usb modem - can't connect

Question

trying to get my Raspberry Pi 3 connected using USA Sprint's modem Franklin U772.

system is:

Linux raspberrypi 4.9.41-v7+ #1023 SMP Tue Aug 8 16:00:15 BST 2017 armv7l GNU/Linux

According to specifications modem offers Ethernet over usb (RNDIS) as connection interface.

Upon plugin modem is succesfully detected and usb0 interface is assigned to RNDIS device, see /var/log/syslog cut:

Feb  2 08:15:09 raspberrypi kernel: [   21.200561] usb 1-1.2: new high-speed USB device number 5 using dwc_otg
Feb  2 08:15:09 raspberrypi kernel: [   21.331448] usb 1-1.2: New USB device found, idVendor=1fac, idProduct=0232
Feb  2 08:15:09 raspberrypi kernel: [   21.331464] usb 1-1.2: New USB device strings: Mfr=2, Product=3, SerialNumber=4
Feb  2 08:15:09 raspberrypi kernel: [   21.331472] usb 1-1.2: Product: Franklin 700 USB Modem
Feb  2 08:15:09 raspberrypi kernel: [   21.331480] usb 1-1.2: Manufacturer: Franklin Wireless Corp.
Feb  2 08:15:09 raspberrypi kernel: [   21.331488] usb 1-1.2: SerialNumber: 0123456789ABCDEF
Feb  2 08:15:09 raspberrypi kernel: [   21.554784] usbcore: registered new interface driver cdc_ether
Feb  2 08:15:09 raspberrypi kernel: [   21.564209] rndis_host 1-1.2:1.0 usb0: register 'rndis_host' at usb-3f980000.usb-1.2, RNDIS device, 7e:25:06:37:b7:31
Feb  2 08:15:09 raspberrypi kernel: [   21.564373] usbcore: registered new interface driver rndis_host
Feb  2 08:15:09 raspberrypi kernel: [   26.022404] usb 1-1.2: USB disconnect, device number 5
Feb  2 08:15:09 raspberrypi kernel: [   26.022603] rndis_host 1-1.2:1.0 usb0: unregister 'rndis_host' usb-3f980000.usb-1.2, RNDIS device
Feb  2 08:15:09 raspberrypi kernel: [   26.400559] usb 1-1.2: new high-speed USB device number 6 using dwc_otg
Feb  2 08:15:09 raspberrypi kernel: [   26.541424] usb 1-1.2: New USB device found, idVendor=1fac, idProduct=0232
Feb  2 08:15:09 raspberrypi kernel: [   26.541436] usb 1-1.2: New USB device strings: Mfr=2, Product=3, SerialNumber=4
Feb  2 08:15:09 raspberrypi kernel: [   26.541444] usb 1-1.2: Product: Franklin 700 USB Modem
Feb  2 08:15:09 raspberrypi kernel: [   26.541452] usb 1-1.2: Manufacturer: Franklin Wireless Corp.
Feb  2 08:15:09 raspberrypi kernel: [   26.541460] usb 1-1.2: SerialNumber: 0123456789ABCDEF
Feb  2 08:15:09 raspberrypi kernel: [   26.566812] rndis_host 1-1.2:1.0 usb0: register 'rndis_host' at usb-3f980000.usb-1.2, RNDIS device, 96:e9:5e:81:6b:bd
Feb  2 08:15:09 raspberrypi kernel: [   26.619390] cdc_acm 1-1.2:1.2: ttyACM0: USB ACM device
Feb  2 08:15:09 raspberrypi kernel: [   26.623541] usbcore: registered new interface driver cdc_acm
Feb  2 08:15:09 raspberrypi kernel: [   26.623549] cdc_acm: USB Abstract Control Model driver for USB modems and ISDN adapters

I put into /etc/network/interfaces:

iface usb0 inet dhcp

ifconfig -a shows:

usb0: flags=4098<BROADCAST,MULTICAST>  mtu 1500
        ether 72:72:02:b1:0a:4c  txqueuelen 1000  (Ethernet)
        RX packets 0  bytes 0 (0.0 B)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 0  bytes 0 (0.0 B)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

now trying to raise interface: sudo ifup usb0:

Internet Systems Consortium DHCP Client 4.3.5
Copyright 2004-2016 Internet Systems Consortium.
All rights reserved.
For info, please visit https://www.isc.org/software/dhcp/

/etc/dhcp/dhclient.conf line 15: option definitions may only appear in the outermost scope.
option rfc3442-classless-static-routes code 
                                        ^
Listening on LPF/eth0/b8:27:eb:82:21:0e
Sending on   LPF/eth0/b8:27:eb:82:21:0e
Listening on LPF/usb0/72:72:02:b1:0a:4c
Sending on   LPF/usb0/72:72:02:b1:0a:4c
Sending on   Socket/fallback
DHCPDISCOVER on eth0 to 255.255.255.255 port 67 interval 4
DHCPDISCOVER on usb0 to 255.255.255.255 port 67 interval 3
DHCPREQUEST of 192.168.10.2 on usb0 to 255.255.255.255 port 67
DHCPOFFER of 192.168.10.2 from 192.168.10.1
DHCPACK of 192.168.10.2 from 192.168.10.1
Too few arguments.
Too few arguments.
bound to 192.168.10.2 -- renewal in 381879 seconds.

Interface is up with IP of 192.168.10.2, but it is not connected to internet: ping -c 5 -I usb0 8.8.8.8

PING 8.8.8.8 (8.8.8.8) from 192.168.10.2 usb0: 56(84) bytes of data.

--- 8.8.8.8 ping statistics ---
5 packets transmitted, 0 received, 100% packet loss, time 4181ms

however, web server, running on modem (192.168.10.1) is up and shows connection is on.

Upd:

I can ping 102.168.10.1 thru usb0.

route -n:

Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
0.0.0.0         192.168.168.1   0.0.0.0         UG    0      0        0 eth0
192.168.3.0     0.0.0.0         255.255.255.0   U     0      0        0 wlan0
192.168.10.0    0.0.0.0         255.255.255.0   U     0      0        0 usb0
192.168.168.0   0.0.0.0         255.255.255.0   U     0      0        0 eth0

What should be done to make it work?

Thanks in advance!