There is a huge amount of discussion on this page regarding whether the A is necessary here in AL hospital. This is not personal A, it is the normal preposition a. Note in the RAE dictionary link below, definition states the llamar can be use transitively (i.e. no preposition is used before the direct object) or intransitively (with the preposition A)
So everybody is right, unless they implied that the way they suggested using A or not is mandatory, because it isn't ... is is optional. In all likelihood various regions have "their way"or doing it so even some natives can believe they know the answer when in reality they only know what they do and what they have heard in their region. :)
Exactly. In this case, the rule is simple: "llamar" always needs the preposition "a" when referring to the receiver of the call.
There are another couple of frequent prepositions: "por" and "en", a couple of examples: - llamar por teléfono, por radio, por megafonía: call on the phone, by radio, by PA - llamar en vano: call in vain
@seamus64: 'they will call at the hospital' meaning "they will visit the hospital": visitarán el hospital. [Edited]
That's a figurative sense of 'call' (from when you'd show up at someone's house and call out to see whether anyone was home), that's specific to English, as far as I can tell. At any rate, I'm pretty sure 'llamar' can't be used in that sense, so you'd have to say something like "ellos van a pasar por el hospital". Could a native speaker confirm please?
Because in this case "a" works as a preposition and you need to used it in order to create a connection between the words, otherwise this would be understood as two different sentences with no practical sense as "Ellos van a llamar - El hospital". So you use "a" and using "a" preposition + "el" goes "al" as a contraction that only works with "a"+"el", like:
A + el + supermercado = al supermercado = to the supermarket
A + el + banco = al banco = to the bank
A + el + hotel = al hotel = to the hotel
A + la + casa = a la casa = to the house (note that it only works with a+el).
Hope i was helpful :)