calling is good. though, they don't like shadows as much as they did before because of teh new privacy laws, and doctors never really enjoyed having a tag-along.
when i was in high school i was in this program that allowed us to shadow doctors for a week...i got to see open heart surgery (awesome), I got see a cathater (ewww), and other stuff...oh well, a friend of mine's best friend is a doc so i have that angle maybe
One of the best things I think is to find a free clinic and ask to volunteer there - a lot of doctors like "chaperones" in the rooms with them for legal reasons, especially if there are invasive exams going on - I chaperoned in a prenatal clinic - got to see tons of stuff and it was sort of like shadowing, but I actually had a role and I didn't feel like a big dork following people around.
Many hospitals have programs where you can volunteer in the emergency department or another department (although a lot don't let people volunteer in the MICU). You'll do things like helping out the nurses or patient transport. From there you may be able to come into contact with some doctors to shadow or see surgeries. Check out the local hospital's website or just call.
Most hospitals should have a volunteer dept for you to contact. When the director of the volunteer dept at my local hospital found out I was pre-med, she placed me into their pre-medical program that allowed me to shadow doctors and sit in on resident luncheon. Some hospitals have such programs but don't publicize it well (if at all). You just have to ask.