Umm, if it's been less than month, don't call. If it's been at least a month you should send a letter updating you recent accomplishments. Do not call or write unless you have something of value to add.
What you should do is call requesting to talk to someone about the WL process at the schools. Be sure to get someone who is in the decision making process. Ask how they use the WL. These may seem like "dumb" questions, but every school does it differently. Ask if it's ranked; ask how quickly they go to the waitlist and so forth.
While on the phone reiterate your desire to attend and WHY. Too many applicants say they want to attend, but the why needs to tie back to your application and personal statement.
As you said, it's late to do so, but this year WL movement has been a lot for many schools.
Hope this helps.