iPad Mini internet connection (No WiFi)
In the US - all iPads (including the mini) are unlocked, pay as you please, no contract devices. The two models of mini are A1454 and A1455 with similar GSM 3G coverage:


Model A1454


GSM/EDGE (850, 900, 1800, 1900 MHz)
UMTS/HSPA+/DC-HSDPA (850, 900, 1900, 2100 MHz)
LTE (Bands 4 and 17)

Model A1455


CDMA EV-DO Rev. A and Rev. B (800, 1900, 2100 MHz)
GSM/EDGE (850, 900, 1800, 1900 MHz)
UMTS/HSPA+/DC-HSDPA (850, 900, 1900, 2100 MHz) 
LTE (Bands 1, 3, 5, 13, 25)



http://www.apple.com/ipad-mini/specs/

Accordingly, you can pick whether want to optimize your LTE future bands (or travel bands) or choose a CDMA+GSM model or the GSM only model. Since there are very few countries with CDMA coverage out side the USA, most people end up shopping the AT&amp;T model 1454 - but curiously, the CDMA model 1455 matches many foreign LTE deployments and plans, so it's a bit of a tradeoff which any one person might prefer world wide.