Not that surprising.
AT&T's been really modernizing their US UMTS/HSPA+ network moving the transport from the cell sites to the core network to VoIP (Carrier Ethernet over VoIP). VZW is doing the same on their upgraded network /w the 4G LTE roll-out. (They only started this when they have moved recently the majority of their metro switching to VoIP which finished recently.)
Hint: Voice is cheap as molasses (think about VoIP) for ALL carriers.
T-Mobile's has had unlimited for ever, and Sprint has unlimited voice as well...
Let's see how long VZW holds out.
I'm most definitely NOT a VZW employee. If a post answered your question, please mark it as the answer.