Yes, it's true! Krys, who played Embry Call in Twilight, was Jacob Black.
Unfortunately he lost the role to Taylor. I've been trying to find an actual source but most Twilight fans have said this on various forums.
Another actor was also switched when Twilight was filming. Emmett Cullen was supposed to be played by another actor but the author stepped in and said no.
So they found another actor, Kellan Lutz. I also couldn't find a source for this one too. The Twilight fans who've been following this movie, since its inception, know this to be true.
I can't really say why Krys lost the role but they did the same thing to another actor.
They seem to be making the same decisions for New Moon. Who knows what will happen for the next film Eclipse, releasing June 30, 2010.
Taylor could've lost the his role, Solomon (Sam Uley) and Krys (Embry Call) seem to have both lost their respected roles.
It's kind of obvious if you think about it. The author, Stephanie Meyer, suggested that Steven Strait should play Jacob.
Yes, the guy from 10,000 BC is Jacob Black. Her other suggestions for the rest of the characters can be found on her website.
Good thing she wasn't the casting director! Although she did have influence on their decisions.
All I can really say is that most Twilight fans, including the author, don't care about casting actual Natives.
As long as they fit the requirement of being "hot." They're good to go. The rest can be faked (a tan and dyed hair).
This posting casts further doubt on the idea that Lautner's "tween" following made him the best choice. If that had been true, he would've been a top choice, not a bottom choice. I don't know why the producers rejected all the Native actors, but it seems they didn't choose Lautner because he was so obviously marketable.
P.S. "Solomon" is actor Solomon Trimble, of course. Actor "Krys" apparently goes by only a single name.
Below: "Okay, so I wasn't their first, second, or third choice. I was only their 100th choice. I still rock, dude!"