When upgrading your cell phone checkout Amazon's prices. They are usually lower than what Verizon, AT&T and the others offer. And its no problem to do your upgrade through Amazon's website.
Better yet see if any of the "free" phones that your carrier offers will meet your needs. There are plenty of Droids and even the oldest iPhone for free out there. Do you really need the latest and greatest phone every few years?
Or, possibly even better, checkout some of the low-cost cell phone companies like Cricket or Republic and see if they will meet your needs. The phones and the service aren't as good as the big name companies, but they might work for you if you are a light user.