What kernel do you have ?
If you read
http://www.motorola.com/softmodem/pu...User_Guide.pdf
it mentions the kernel versions for different distributions maybe you can get a driver for
another distribution.
Even if you have a newer kernel sometimes modprobing the module works.
When i had my sm56 (long ago) i had the same module and i used it from newer kernels
as well (until one kernel that some functions changed and it didn't work anymore)
Even if you manage the driver to work, the perfomance is horrible (at least in my case and
also a friend of mine)
I suggest a hardware rs232 (external serial modem) modem.