Why can't I talk and browse the web simultaneously on Sprint?

Episode 1127 (1:55:00)

Rick from Kansas City, MO
iPhone 6 and 6 Plus

Rick says that he hears that with Sprint, if they upgrade to the new iPhone, they won't be able to talk and surf at the same time. Leo says that he can on AT&T and Verizon, though. Verizon moved over to Voice Over LTE and Leo thought Sprint was moving that way too, but apparently they haven't. T-Mobile will also work. Any GSM network will do it, and Leo suspects that Sprint will eventually go that way.