A company who has been doing ram upgrades to other PDAs in the past (iPaq, etc) may soon be offering an upgrade for the Axim. This is not a plug-in card. They actually install more ram in the unit itself, leaving the expansion slots still available. For example, they offer a 256 meg upgrade for certain iPaq models.
http://www.times2tech.com/
Perhaps if a lot of Axim users contacted them with interest in this, they would consider it worthy of higher priority to make it available.