[Thunderbolt Q&A, Help & Troubleshooting] loonatik78:
I'm saying there's not such thing as an EHRPD tower. You've got CDMA towers and you've got LTE. These technologies are VERY different. Let me try to break this down. I probably should have explained it better above.

First, for the record, for cost considerations, LTE and CDMA for Verizon come off the same physical towers. There's not much point in erecting different towers for different antennas if they're still physical space on existing towers.

So... from the beginning...

Verizon runs to completely separate networks today. One is based on CDMA technology, one on LTE. Let me start first with CDMA.

CDMA, otherwise known as Code Division Multiple Access, is a method of physically transmitting a signal to and from a device. Verizon implements asynchronous CDMA to avoid issues with doppler shift in the signal frequency and speed of light delay from transmission to reception. CDMA is the radio access technology, NOT the protocol. The protocol is a patented technology known as cdma2000 and uses the CDMA radio access method as it's base layer.

cdma2000 is the protocol and encompasses a number of transmission protocols. Those would include IS-95, 1xRTT, 1xEV-DO, and the 1xEV-DO revisions 0, A, and B. To clarify, 1xEV-DO stands for single channel evolved-data optimized. EHRPD is a subset data transmission protocol of revision A of 1xEV-DO. I believe that Verizon didn't implement EHRPD very widely in it's deployment of EV-DO rev.A because at the point of first introduction their path of evolution was undecided. They very well could have moved on with EV-DO rev. B and attained speeds comparable to WiMax while being able to upgrade many of the existing CDMA handsets with new firmware to utilize the newer revision, just as had been done when rev. A came. One of the issues with cdma2000 is that the protocols aren't compatible. EV-DO used to stand for Evolution-Data Only, because data is all it does. When the devices is used for a voice call, it must switch protocol modes back to IS-95 to interface with the switch-based voice network on the backside of the tower. This is why CDMA devices cannot do data while in call.

LTE is a completely different technology altogether. It's an evolution of GSM, and accordingly, expands upon the basic technology of GSM. The base of GSM is TDMA, Time Division Multiple Access. Each device has a time slot that it's allowed to transmit or receive data on, usually a small fraction of a second. LTE also makes use of FDMA, Frequency Division Multiple Access, meaning that there are many frequencies that can be used to address different devices.

LTE makes uses of protocols, some similar to GSM protocols, to transmit and receive data. These are described in the LTE specification, and as time passes, additional LTE protocol specifications will be added, such as LTE Advance.

The goal of Verizon is to have a pure LTE network in the future. LTE is not simply a data transmission technology, but rather a full blown cellular standard just as GSM is, and as such can carry voice. When it does, voice will be basically VoIP, as LTE is a completely packet based technology and doesn't depend upon network switching (unlike IS-95 and 1xRTT, which is still the voice carrier technology supported by cdma2000). Carriers like this because it makes upgrading and scaling the network easier. The end result will be a more seamless user experience and the ability to integrate native voice features into data features of the device.

Modern LTE devices accomplish voice and data by using 2 different radios. In the Thunderbolt, that would be the CDMA radio built into the MSM8655 Soc processor and the MDM9600 LTE modem chip. Currently, this is the ONLY combination of chips that allows full simultaneous voice and data over the entire network. Unless the LTE chip of the devices handles both CDMA and LTE, AND can interlink with the SoC radio to manage SAR power limits, this will remain the case. Currently, only Qualcomm chipsets accomplish this, making the Thunderbolt the most functionally connected device ever sold on Verizon.

If anyone is interested in knowing more, let me know. I'll write up a bit more in-depth primer on these subjects and post it.