Does the R,G,B range varies for the image taken with different cameras. Suppose I capture an image with blackberry and I capture the same image with a digital camera; would the RGB range vary for the image in both scenarios or would it be the same.
Of course it does. Different cameras have different spectral responisivities, different exposures, different gammas, different algorithms they apply to "improve" the image for you, etc. Don't think that if you take a photo of, say, the x-rite Color Checker Chart (a standard color calibration target), that you will get the nominal sRGB values out. You most certainly will not. Not from your camera or any other camera. You'd need to do a color calibration to post process the image if the sRGB image is what you wanted because all cameras are different.
The sensitivity of different devices varies. And their gammas will possibly differ.
This starts getting into color theory. You can start to see the complexities if you read about a standard designed to work around these problems, http://en.wikipedia.org/wiki/SRGB#The_sRGB_gamut