Smartphones have now entered what you might call the “cannibalism” phase of market growth — which is considerably less disgusting than it sounds, and might even prove to have some advantages for consumers.
MediaPost's marketing blog noted that the “Next wave of [the] Telecom wars [is] to focus on switchers.” In other words: smartphones aren't exactly a “new” thing anymore; pretty much every adult who wants a smartphone has one already.
So if a wireless company wants to increase its subscriber base, there aren't many potential “new” customers out there (“new” meaning, someone who has never owned a smartphone before); instead, it has to convince “old” smartphone users to switch away from their current providers and go with someone else.
Which is not to say that the smartphone industry is on the verge of any huge changes, from consumers' perspective. Indeed, there's some inherent limits to how much competition can exist between various smartphone companies, anyway.
For example: AT&T and T-Mobile have both been targeting each others' subscribers — because the two companies use the same technology, so switching between the two is easy. But companies like Sprint and Verizon Wireless use different technology.
But regardless of what smartphone plan you have or which company you go with, it's always worth periodically comparing your subscription to other available offers. In many cases, merely letting your provider know you're switching to a cheaper service can inspire your current provider to make a better counteroffer.