Ive called in two. My friend called in one. My method is to call loudly for at least an hour without stopping. Im not claiming to be an expert but Ive had success this way. The first bear I called...

I used a 350 rem mag with 225 Nosler Partition handloads on this bear. Ive taken a couple with it. It just flattens them.

Took the guy while he was feeding on Choke Cherries. Great way to start the 2012 hunting season.
http://i4.photobucket.com/albums/y136/Sprayer/DSC01091.jpg...