You need to make sure that the modules are loaded into the kernel.
See the README or INSTALL file that comes with the ltmodem driver for how to do this.
Basically, the install script copies the files to /lib/modules/kernelversion/somewhere and then runs
to check the dependencies. You can then load the modules with
Code:
modprobe ltserial
modprobe ltmodem
or by setting up lines in /etc/modules.conf
If there are any errors loading the modules, you can read them in /var/log/messages.
Note also that your kernel must be compiled with loadable module support (pretty much all distros ship with this option turned on, but if you recompiled the kernel yourself then you may need to check this).
Hope that's of some help,
— Robert J. Lee