I can't see there being an issue as far as the card networks are concerned with guards being issued with a mobile-enabled terminal which they can use. Iarnród Éireann does this. The guards probably won't be best pleased carrying another piece of kit around though!
ATM-only cards will not work at a point of sale terminal, whether swiped, chip read, or keyed. (Most don't even have a 16-digit PAN.)
Visa Electron cards are not accepted by the railway, except by a few TOCs at their booking offices and TVMs only. Where they are accepted they cannot be used on a manual imprinter as they do not (or should not) have embossed numbers. They can be chip-read, or swiped if a chip is not present or defective. I forget whether they're allowed to be key-entered.
Dual SIM GSM card terminals are not common.
ATM-only cards will not work at a point of sale terminal, whether swiped, chip read, or keyed. (Most don't even have a 16-digit PAN.)
Visa Electron cards are not accepted by the railway, except by a few TOCs at their booking offices and TVMs only. Where they are accepted they cannot be used on a manual imprinter as they do not (or should not) have embossed numbers. They can be chip-read, or swiped if a chip is not present or defective. I forget whether they're allowed to be key-entered.
Dual SIM GSM card terminals are not common.