A Linux MWave Modem driver 'mwave' can be found in kernel 2.4.11 and later
In addition to the kernel driver you will need some userland utilities (MWave Manager) that can be found here: http://sourceforge.net/projects/acpmodem/
SUSE and Debian include these utilities in the 'mwavem' package. The package is in the non-free section of the Debian archives because it includes downloadable DSP software for which no source code is available.
Note: the driver is incompatible with ACPI due to its use of a proprietary SMAPI interface. This SMAPI interface is disabled if ACPI is enabled. ACPI must be disabled by use of the "acpi=off" kernel boot parameter. Use APM instead. IBM recommends APM over ACPI on these machines anyway.