No certain brand, but do make sure it is for pay phone calls. Get one with lots of minutes, or one you can re-charge. Check the card to see how many minutes are "gobbled" up just to make the call.
You should go ahead and activate the card before sending it, then give your recruit any necessary info s/he will need to use it. It will save them time when making their first call.
My son bought an activated phone card at NEX once he was at GL.
we got ours a penny talk ..... we found it at Walgreens ,... i can go online and add minutes if needed