I'm confused as to how you think changing your broadband supplier will stop you getting calls on your phone line? Even changing your phone line supplier isn't going to make any difference unless you change your phone number (the people calling you don't know and don't care what phone company you get service from).
First try *76 on your phone line - this will stop all anonymous calls. Having done this I get an insignificant number of spam calls, and no spam faxes despite having had a listed phone number for 8 years.
(It's the "Block the Blocker" service:
http://www.pccw.com/eng/Products/For...e-Blocker.html )
Beyond that, what exactly would you like your telephone supplier to do? Do you want to give them a list of all the phone numbers which you will accept calls from and to block all the rest or what?