Several coworkers had truly unlimited data grandfathered through older contracts, but ultimately decided that voting with their dollars for a decent company/policy was more important for what might have been very little (if any) additional cost per month.
This is what has me switching. Despite an expected increase of about $10/mo, I'm moving to T-Mobile as soon as the weather turns nice (unnecessary transport in Minnesota winters is... undesirable) because I don't want to give my money to a company actively fighting against net neutrality, Verizon. Plus the bonus of influencing the mobile market in a positive manner, as this article describes.