I would try to add it in post like others have suggested giving you more freedom rather than intentionally getting digital noise. The film grain slider in lightroom works quite nicely, but haven't tried printing any images where I've used 'film grain' so not sure if it prints well yet.
I also went through a stage of trying out 'push processing' on digital by effectively underexposing my shots by two stops and then overexposing in lightroom to get the film grain look. That worked to a certain extent but not as nice as push processing on proper film!
Mark.