Although there is no Standard American Pronunciation

VOA Special English can be used for ESL learners as a standard pronunciation, can it?

Here's an interestin article on the definition of Standard American English:

Ask a group of experts to define Standard American English, and you'll find, paradoxically, there's no standard answer. Even the editors of The American Heritage Dictionary are careful to qualify their definition. They note:

People who invoke the term Standard English rarely make clear what they have in mind by it, and tend to slur over the inconvenient ambiguities that are inherent in the term.
American Heritage goes on to explain that the term:

is highly elastic and variable, since what counts as Standard English will depend on both the locality and the particular varieties that Standard English is being contrasted with. A form that is considered standard in one region may be nonstandard in another...
Where does this leave us? American Heritage suggests there's no single, universally accepted standard for how to speak or write American English. Even so, school systems, professional communicators and businesses all have standards and, not surprisingly, the rules (at least for grammar) do not vary dramatically from place to place.


What's more elusive is finding an accent that sets the standard. The variety of English spoken in the nation's Midland areas is often pointed to as sounding most neutral or "mainstream." It's frequently identified as the speech of broadcasters. But as linguist Matthew Gordon explains, it too is not unaccented English. For a variety of reasons, over time, the Midland variety may lose its status as the vox media.

Not Really Real
The "unaccented" variety that is sometimes called Standard American or Standard Speech is one taught by accent coaches. This form is actually an idealized dialect - meaning, it's not really spoken anywhere, but instead is acquired through professional training. Actors and professional communicators (including some from the Midlands!) often take classes in "accent reduction" to lose any regional or social sounds in their speech. It takes a lot of work.

Natalie Baker-Shirer, an accent coach and acting teacher at Carngie Mellon University explains:

"Standard Speech" is spoken nowhere in America, as such. It is based on RP (British Received Pronunciation) which was adopted with American alterations in the early 20th century by linguist William Tilly. These alterations, this authentic "American" sound was loosely based on the speech of North Eastern population of the US. It was spoken by the cultured, well educated, well traveled people of the time. Listen to old movies to hear it.
Baker-Shirer, like The American Heritage Dictionary, qualifies whether this kind of speech is "correct". She writes:

According to Daniel Jones, An English Pronouncing Dictionary, "There are innumerable other ways of pronouncing English in existence, and I do not claim that RP is intrinsically "better" or more "beautiful" than any other form of pronunciation."


http://www.pbs.org/speak/seatosea/standardamerican/