Some schools draw heavily from the waitlist, while others do not. A few of the schools I applied to last cycle had the reputation of waitlisting a lot of applicants and then accepting the ones that showed motivation to attend that school. N = 1, but within 3 weeks of submitting an update letter / letter of interest, I was accepted off the waitlist. So my advice would be to show continued interest. The degree to which schools are receptive of updates / letters of interest / intent varies a fair amount. My advice would be to find out if the schools at which you are waitlisted are receptive to updates and whether or not the draw heavily from the waitlist and if so, when. Show genuine enthusiasm about the schools, but don't be too clingy (i.e. don't call every week). If a school is your number one choice, let them know. Most importantly, be patient. A TON of movement happens in the spring.