I'm trying to choose between the various data plans for an iPad Mini. Based on this chart it appears that the ATT model (A1454) only works in North/South America, while model A1455 is supported worldwide.
For this reason (limitation) I assumed the ATT plan would be least expensive per MB/Month, however it is the most expensive per month:
ATT 250MB per month $14.99 SPRINT 300MB per month $14.99 (better value) Verizon 1GB per month $20.00 (best value)
What is the value in the ATT network or related technology that I'm missing?
Finally, I've been told that GSM operates worldwide, are both these models GSM or CDMA?