The handhelds use a "micro SD card" and the mobiles are SD cards. However, the card will work with an SD card adapter.
As far as moving the micro SD card from the 688 to the 1095 without reformatting and reprogramming -- it *might* work but there are probably (at minimum) some model specific global settings that will be misunderstood.
Ultimately, you probably should consider getting 1 or 2 addition SD cards.
Ok quick update... took my micro SD card out of my pro668 and put in my 1095 (w/ adapter).. works. So I'm thinking that the SD card that was in my 1095 to begin with was bad somehow? Putting the SD card from the 668 hasn't done anything to the 1095. Everything works and I'm hearing things...
Do get a spare card but before you just pitch the old card, try an application called "SD Formatter" on it. The app in the E-Z Scan software isn't very thorough. I've brought several "dead" cards back to life with Formatter.