Disclaimer: I don't know what I'm talking about

I've been cleaning up our company's mismanaged AT&T account, canceling contracts for lost SIMs and cards, getting new cards etc. Unbelievable so few accounts could be such a mess. So, they have told me I could "borrow" a card for a trip to EZE this coming week.

Do I have to call AT&T to have them allow international roaming like you do with a phone? Would there be additional fees beyond the normal monthly charge? (I don't want it to cost the company additional.) Will it work in Argentina?

I could take the regular 875 or an older one with external antenna, but I've got an unassigned 875U (USB connection) arriving tomorrow

I mean once I download the software, theoretically I could borrow a card whenever I travel? At least in the US.

Is this even worth thinking about? What's the potential downside?

Thanks for any help.