I've been struggling with this for a while and wanted to share my success with RAP-5 and ZTE MF668a 3G:
1. Removed PIN lock
2. Disabled USB storage by sending AT+ZCDRUN=8 trough putty to device ZTE NMEA Device
3. Re-Proviosined AP from CLI with following USB parameters:
(A650) (config) #provision-ap usb-dev 0x19d22000
(A650) (config) #provision-ap usb-dial ATD*99#
(A650) (config) #provision-ap usb-type option
(A650) (config) #provision-ap usb-tty ttyUSB2
Rest of the provision commands I just copied from web interfaces view commands list.
Helpful links:
http://community.arubanetworks.com/t5/Remote-Networking/RAP-5WN-with-Huawei-3765-3G-Modem-not-working/td-p/10616
http://3g-modem.wetpaint.com/page/ZTE+AT-commands