A.3. PCMCIA Card Services and Advanced Power Management
Quoted from the PCMCIA-HOWTO:
"Card Services can be compiled with support for APM
(Advanced Power Management) if you've configured your kernel
with APM support. ... The PCMCIA modules will automatically
be configured for APM if a compatible version is detected on
your system. Whether or not APM is configured, you can use
cardctl suspend before suspending your
laptop, and cardctl resume after resuming,
to cleanly shut down and restart your PCMCIA cards. This will
not work with a modem that is in use, because the serial
driver isn't able to save and restore the modem operating
parameters. APM seems to be unstable on some systems. If you
experience trouble with APM and PCMCIA on your system, try to
narrow down the problem to one package or the other before
reporting a bug. Some drivers, notably the PCMCIA SCSI
drivers, cannot recover from a suspend/resume cycle. When
using a PCMCIA SCSI card, always use cardctl
eject prior to suspending the system."
You should use the internal modem in a laptop instead of a PCMCIA modem, if possible (it may be a WinModem).