What is happening here is that yell.com is detecting irregular activity. If you try to do this scraping visually using selenium, the way it would load Javascript:
from selenium import webdriver
from bs4 import BeautifulSoup
driver = webdriver.Firefox()
driver.get(url)
driver.set_window_position(0, 0)
driver.set_window_size(100000, 200000)
driver.execute_script("window.scrollTo(0, document.body.scrollHeight);")
time.sleep(5) # wait to load
# at this point, if you see the Firefox window that opened you will see the message
# Anyway, if you manage to get pass trough that blocking, you could load BeautifulSoup this way:
soup = BeautifulSoup(driver.page_source)