My policy is always to call each and every girl/family. At the tryouts, we let them know when the latest this will be. This year, we had tryouts spanning 2 weekends and told the girls that we would call them all within 48 hours of the last tryout. I personally don't believe in the "if you don't hear from us, you didn't make the team" philosophy, nor am I real crazy about e-mailing, though that's much better than no contact at all.
While we do call or talk to some girls/families right away, the others should not automatically assume they are not wanted. In some cases, we may know of other girls trying out in the near future who might be a better fit for our team and we wouldn't want to ask someone to join the team who might not end up getting much playing time. In other cases, I guess you can say the person is a "second choice", but with so many of the girls going to multiple tryouts, its just the nature of the beast ... similar to getting a job you might not have been the top choice for. I know some people in my company who weren't the first choice but got the opportunity and have had fantastic careers.