All iPhone 5s and iPad minis support GSM. iPad minis are not locked to a carrier, but the iPhone may be depending on where and under what sort of agreement you purchased it. The iPhone will need to either have been purchased unlocked or have been unlocked by the cell carrier to be used with other carriers.
Neither the iPhone nor the iPad wil support a CDMA carrier other than the one for which the device was sold, though.
Regards.