Assuming you have a default Karmic 9.10 setup, it is not visor
/usbserial
module crashing your Palm, but the buggy modem-manager. Following this launchpad bug, all you need is to remove modem-manager
package (and probably reboot).
As there is AFAIK no other way to communicate with your Palm other than through ttyUSB*
, and because everyone report that their Palm syncs successfully, PPP connection should work too (if you won't do weird things with the tty like modem-manager does)