This is a nice Australian movie, some serious stuff, a considerable about of funny stuff. The broad plot is standard: "disadvantaged but talented kids succeed by pluck and perseverance." But it's different enough that it kept me interested and even involved.
Things start in 1960's Australia, where the aboriginal population is still widely discriminated against; if anything, it might be worse than the bad old segregated USA. A group of aboriginal girl singers crash a white-only talent contest; they're clearly better than anyone else, singing Merle Haggard's "Today I Started Loving You Again". But the bigoted judges let a white kid win instead.
This outrages Dave, who's been hired as the Master of Ceremonies. He, like many Australians, is a drunken loser, but he knows talent. He offers to take over as the girls' manager. He demands that they stop doing their beloved country music, and start doing Motown soul. He changes their group's name to "The Sapphires". And before you know it, he and the kids are off to Vietnam, where they are to entertain American troops. What could go wrong? There is, of course, internal bickering and conflict. And it's Vietnam, so: boom.
There is social commentary, but it's not too heavy-handed. It's (very loosely) based on an actual group; Wikipedia has the details. (The article also notes that the DVD cover prominently features the Dave character over the girls—see above—and people got kind of upset about that.)
Where had I seen the actor playing Dave before? Oh, yeah: playing Kristen Wiig's cop sorta-boyfriend in Bridesmaids.