Everything I've been able to learn is that the MPx100 is tri-band (no GSM 850

) and has a MINI-SD Slot. That as opposed to the MPx220 which is quad band (important because I'm a US AT&T Wireless customer) AND a full size SD Slot.
For those reasons, despite personally prefering the candy bar form factor, I'm going with the MPx220. Of course, the initial reported specs on each of these units may be wrong, which is why I reserve the right to change my mind :P
One thing is for sure......I will be buying eirther the 100 or 200 MPx and I can't wait until they're here (especiallyonce AT&T has them).