Simple. Off load more people to LTE networks. Notice voice calls drop calls down to wcdma even with LTE iPhone.
So those using LTE pure data on iPhone 5 are not interfering with wcdma voice calls.
I am sure drop calls are improving in NYC with AT&T as more and more people get LTE devices.
Verizon CDMA tech could always handle voice better. And CDMA handles tower handoff much better.
But verizon is transitioning to pure LTE voice and data in the next 1-2 years. CDMA voice will be around probably till 2017-2019 at this rate.
Nice breakdown, thanks