Verizon has a service that allows you to block calls, and they charge you for that. I've been using Easy Filter (I got it for free on the market place) for a good while now and there have been no charges on my bill.
Easier than paying for an app...your Droid X already has this function built-in..kinda sorta..
1) Make a new contact labled "Telemarketers"..
2) Under that contacts Menu, select "send straight to voicemail"
3) Each time you recieve a call from one, add that number to that contact under the Menu for that contact
Its a bit time consuming, and you do have to take 1 call from each one, but it is free afterall...and free is always good IMHO...