Very Important: Did you trade in a phone? If not this does not apply to you:
VZW got smart about trade-in credit. It is applied as a pro-rated monthly amount not as an upfront savings If you cancel your account with them, you forfeit the amount remaining uncredited.
So if you took advantage of a trade, you'll lose the value if you switch carriers 'cause you won't continue receiving that monthly credit.
I'm with VZW and got $200 in trade when I bought my OG XL w/ payments of $32/month. Included on my bill is an $8 credit for the trade ($200 over 24 months). Phone "costs" me $24/month. I still owe for half the phone's total value however, 'cause I "paid" $32/month towards it ie $760/2 = $380. IF I pay off the phone now, it'll cost me the full $380. If I continue to do payments, I'll be out of pocket $280 because of that $8/month credit. Over the 2 years, then, I will have paid full price on the phone BUT recouped the $200 trade value.
I am continuing to make my payments. I bought my 2 XL from Google so I did NOT have to pay off the OG XL had I gotten it from VZW.