Actually the usbserial module has been added to the kernal in ubuntu 9.04 (jaunty). Everyone using a phone or usb device to access internet will be having problem with that. To solve this please follow the following steps.
It is possible to pass the ids as kernel parameters.
1. Get your device’s vendor and product ids. Connect your device and type at terminal:
$ sudo lsusb
2. Open your menu.lst file to edit.
$ sudo gedit /boot/grub/menu.lst
3. Find your ubuntu kernel line.
kernel /boot/vmlinuz-2.6.28-13-generic root=UUID=c54f5577-285d-455d-8……
4. Add this line below it
usbserial.vendor=0xVVVV usbserial.product=0xPPPP
where VVVV and PPPP are vendor and product ids.
Restart your system, for the changes to take effect….
Now you need not modeprobe after connecting your device