Right now, almost all LTE chips everyone is using are from Qualcomm. Qualcomm has voice features that integrate with their CPU's - without that you don't get voice over over the cell network. The MDM9600 in the "new" iPad is this way, so an even newer chip would be needed in an "iPhone 5":
Right now, pretty much every 4G LTE phone has two entirely separate cell network chips, antennas, etc. which is the main reason battery life is so bad. When we get better integration of components and smaller chips, we'll get over the "bad battery life" hump.
http://www.anandtech.com/show/4925/why-no-lte-iphone-5-blame...
Right now, pretty much every 4G LTE phone has two entirely separate cell network chips, antennas, etc. which is the main reason battery life is so bad. When we get better integration of components and smaller chips, we'll get over the "bad battery life" hump.