Sprint is a distant third in the iPhone market. In a somewhat desperate move, they have launched a series of ads about their unlimited data plans.
I still have unlimited data with AT&T. I have not exactly been ecstatic about the service, but I have stayed with them. Verizon seems to be more popular these days, but AT&T has marginally better coverage in the areas I care about. More to the point, switching plans is a marginal pain, and I have never seen a reason to bother.
Is unlimited data worthwhile to me? No. I'd drop it in a heartbeat if a better offer came by. So what would it take?
UNLOCK. MY. PHONE.
I paid for an expensive phone and I cannot take it with me we when I change networks. That irritates me immensely. Sprint, unlock my phone, and I'll switch to your network in a heartbeat.