i work at verizon, and they've disappointed me a few times this year:
first when they gave and then took away the $15 data plan option. a lot of our customers don't need unlimited data and it was a great alternative to paying $30 a month.
Then they changed their warranty replacement methods. It was free overnight shipping, then you have 10 days to return the phone. NOW, it's 3-5 days via USPS and you only have 5 days to return the old phone. Then they pour a little salt in the wound by texting the customer right after they receive the phone telling them they are going to be charged a 300-500 dollar equipment fee if they don't return it. Well the problem with that is, most customers read this wrong and think they ARE being charged the fee. You don't know how many pissed off people i get calling the store about this on a daily basis.
when i first got verizon about 5 years ago, they had EXCELLENT customer service. it's really gone downhill in the past year.... disappointing.
but, more relevant to the discussion at hand:
if you have an unlimited data plan now, don't worry. verizon won't change your plan unless you agree to it, EVEN IF YOU UPGRADE YOUR PHONE (renew your contract). i have a couple customers that still have unlimited usage on mobile broadband cards from years ago, and i've upgraded them into a mifi and kept the unlimited plan.
as for switching to another carrier, all you're doing is paying extra money (by switching) to delay the inevitable for a short time. It's only a matter of time before t-mobile and sprint jump on the bandwagon.