Hello Leo,
the following steps are for ZM2110(CDMA), I tested them on android 4.2.2, I think they should be useful for you !
-----------------
(1) Replace original file with libreference-ril.so file that ZTE released.
(2)Copy init.gprs-pppd file to system/etc/ppp directory
(3)Modify init..rc like following:
service ril-daemon /system/bin/rild -l /system/lib/libreference-ril.so -- -d /dev/ttyUSB20 -u /dev/ttyUSB0
class main
socket rild stream 660 root radio
socket rild-debug stream 660 radio system
socket rild-ppp stream 660 radio system
user root
group radio cache inet misc audio sdcard_rw log
service pppd_gprs /etc/ppp/init.gprs-pppd
class main
user root
group radio cache inet misc
disabled
oneshot
Good luck!
Regards,
Weidong