I live in an area where there are three internet/TV providers. So, not only do I threaten to cancel, I actually do cancel and switch to take advantage of new member promos. Since I have one Tivo with a cablecard and connections to all three providers, switching is relatively easy.
Of course, after I cancel, I get great offers from whomever I switched away from, but they’ve gotten much more stingy in giving me those offers before I switch.
My typical all-in internet/TV bill including equipment has been $75-$85 for the past several years. Obviously that is market and competition dependent.
For auto/home/umbrella insurance, I shop around every year and have switched when another provider saves me more than a couple hundred or so a year. On average, I have switched about once every 3 years or so. There’s no negotiation since rates are set in advance, but it does pay to shop around.
For mobile phone, it just pays to be on top of what current offerings are. Often, you can switch plans with the same provider to take advantage of current plans/discounts.