Okay, It's look like, BT4 team still doesn't give any solution for this.
Before this, i've already make one post about this a few day before bt4 beta forum disappear. I'll write it once again >.< because, some people look like need it. A lot of usb dual mode modem can be detected this way. like GlobalSurfer, GlobalTrotter, iCON, Hyundai, and some Phone modem. WOW.

Bt4 pre Final still doesn't detect any usb dual mode modem. This distro just detect the storage device. so what you need is usb_modeswitch.
note: Sorry i can't write any url yet. and this must be run as root !!!!
Code:
wget *****************************usb_modeswitch-1.0.2.tar.bz2
tar -xjf usb_modeswitch-1.0.2.tar.bz2
cd usb_modeswitch-1.0.2
make install
The out put must be something like this
Code:
mkdir -p /usr/sbin
install ./usb_modeswitch /usr/sbin
mkdir -p /etc
install ./usb_modeswitch.conf /etc
After that you need to open the usb modeswitch configuration. (i use kate)

Code:
kate /etc/usb_modeswitch.conf
look for your device in there. Someone out this post looking for AC8710, there is settings for ac8710 in this configuration. You should find it and remove any " ; " in the front of any line your usb modem section. for another example, i'm using ZTE AC2726. woopsssssssss theres nothing about ac2726 in there, it's okay, what i need is looking for my device vendor and product id first. i can using lsusb and dmesg for this. I get that my ZTE ac2726 vendor is 19d2 and product id fff1 for modem and fff5 for the storage media. then i'm looking what siliar to it. and i found :

Code:
########################################################
# ZTE AC2710 (EVDO)
#
# Contributor: Wasim Baig

;DefaultVendor=  0x19d2
;DefaultProduct= 0xfff5

;TargetVendor=   0x19d2
;TargetProduct=  0xffff


;MessageContent="5553424312345678c00000008000069f010000000000000000000000000000"
It's nearly look like My usb modem. so..... i wrap it and copy it. paste it in the bottom and edit it. It's Look like this :
Code:
########################################################
# ZTE AC2710 (EVDO)
#
# Contributor: Wasim Baig

;DefaultVendor=  0x19d2
;DefaultProduct= 0xfff5

;TargetVendor=   0x19d2
;TargetProduct=  0xffff


;MessageContent="5553424312345678c00000008000069f010000000000000000000000000000"

########################################################
# ZTE AC2726 (EVDO)
#
# Contributor: Wasim Baig

DefaultVendor=  0x19d2
DefaultProduct= 0xfff5

TargetVendor=   0x19d2
TargetProduct=  0xfff1


MessageContent="5553424312345678c00000008000069f010000000000000000000000000000"
remove the ";" after edit it. Don't forget !!
Okay now my job was done. Just plug your device (usb dual mode modem) and then :

Code:
usb_modeswitch
Then the output should be something like this :
Code:
 * usb_modeswitch: tool for controlling "flip flop" mode USB devices
 * Version 1.0.2 (C) Josua Dietze 2009
 * Works with libusb 0.1.12 and probably other versions

Looking for target devices ...
 No devices in target mode or class found
Looking for default devices ...
 Found default devices (1)
Accessing device 004 on bus 003 ...
Using endpoints 0x0a (out) and 0x89 (in)
Inquiring device details; driver will be detached ...
Looking for active driver ...
 OK, driver found ("usb-storage")
 OK, driver "usb-storage" detached

Received inquiry data (detailed identification)
-------------------------
  Vendor String: ZTE
 Product String: USB Storage FFF1
Revision String: 2.31
-------------------------

Device description data (identification)
-------------------------
Manufacturer: ZTE, Incorporated
     Product: USB Storage
  Serial No.: 000000000002
-------------------------
Setting up communication with interface 0 ...
Trying to send the message to endpoint 0x0a ...
 OK, message successfully sent
Device is gone, skipping further steps ...
-> Run lsusb to note any changes. Bye.
then.....
look at dmesg is there something about ttyUSB0 or ttyACM0 ? chek lsusb too. if ther is still nothing look like that, what you need to do is modprobe !!

Code:
modprobe usbserial vendor=<YourTargetVendID> product=<YourTargetProdID>
check again in lsusb and dmesg.
You now should be seeing something about ttyUSB0 or ttyACM0 in dmesg. so.... there is your modem.

Last thing you need is dial to the provider, you can using gnome-ppp or kppp or just wvdial. i'm using wvdial coz it's more easy for me >.< look about wvdial at another thread. here just about usb dual mode modem. But, if someone might want to ask something, i'll look what i can do.

Sorry for bad english. Hope this usefull.

Regards,
JoeleZ