all of the answers given for land line are used here in buenos aires. you can use "línea fija" but usually i´ve heard it one of these ways:
"llamáme al fijo, por favor."
¿tenés un teléfono de línea?
if you want to buy a card to CALL LOCALLY from a land line at the quiosco, you probably want to use one from your telephone company (telecom or telefónica). "una tarjeta de telefónica para hacer llamadas del fijo"
i´ve never used llamada directa or hable más for locals calls - i think they are more for calling abroad.
to my knowledge, the only cell phone cards are by brand so either: claro, movistar or personal. (i don´t think nextel has cards.)
so i agree with steveinbsas that it´s easier to ask for a specific brand and if they don´t have it, see what else they have.