[Motorola Triumph] rune-san:
Just to expound on this, the idea here is just a bit more complicated on simultaneous voice and data (you're exactly right and I dont mean to offend at all, I'm just adding to your point).

SVDO as you mentioned, and LTE, are two different things in the idea of simultaneous voice and data. SVDO, as you already said, allows a 1x and EVDO session to occur simultaneously, and requires the chipset to support it. The problem is that very very few actually do. The thunderbolt is one such phone, but it only does it in very specific circumstances and in a special way.

LTE is an IP-based technology, and therefore treats voice and data the same (like GSM).

That being said, VoLTE (Voice over LTE) is not an easy road because of the difference between 3G and 1x (circuit switched networks), vs. LTE networks (IP based). Because of these huge differences, bridging equipment must be used to work with the handoffs of calls between the networks. This process on phones is called eHPRD and is in place on all current Verizon 4G phones. This process will not actually be used though and is an empty feature. This process is so complex that Verizon has said that their VoLTE system will NOT be doing handoffs to 3G or 1x. Calls placed and received on 4G LTE networks must remain on the network. That is why for now, Verizon's LTE ONLY handles data, Verizon is not initiating VoLTE until the first half of next year.

Also keep in mind that while LTE + 1x voice is *technically* simultaneous voice and data, it is not SVDO in the sense of the acronym, which refers to sending voice and data over the same bands by using spare frequency from a 3G data session to "squeeze in" a 1x voice band in the space where previously, a entire 3G band would have been placed. LTE + 1x voice is really no different from using Wifi + 1x voice. Both rely on the idea of using 2 entirely separate bands for a voice and data session rather than squeezing a voice and data session into 1 band.

The thunderbolt can do SVDO because it has 2 radios (and a proper radio firmware to enable SVDO and allow the two radios to work as 1). The qualcomm processor + radio (MSM8655) gives the phone its 1Ghz processor and the capability of 3G and 1x (but only 1x is used on the Thunderbolt); and then a second qualcomm radio (MDM9600 Gobi Radio commonly used on 4G mobile broadband cards) capable of LTE and 3G. That's why it has antennas literally bursting at the seams (and into the battery cover), and why its battery life is amongst the worst of all the 4G phones. A call received on the Thunderbolt always goes to the 1x radio on the MSM8655 processor. 3G and 1x treat data and voice separately, with 1x capable of voice or data and 3G capable of simultaneous voice and data only if SVDO is supported on the chipset (the thunderbolt nor any other 4G verizon phone support SVDO on a single chipset, the thunderbolt is able to do it with multiple chipsets). I'd make a table, but I'm not really sure how to, so in case my rambling on was a bit confusing, I'm going to lay out a concise list assuming Wifi isn't being used (which as said above is similar to LTE + Voice on current networks) That will change next year.

Verizon Thunderbolt:

When in a 4G LTE zone:

Data is sent over the 4G LTE radio from the MDM9600, while received or placed calls to the phone go over the built-in 1x radio in the MSM8655.​

When only 3G is available:

SVDO is activated through software. Data is sent over the 3G radio from the MDM9600, while received or placed calls to the phone go over the built-in 1x radio in the MSM8655. The 1x band for the call is squeezed into the same band as the 3G data session using SVDO.​

When only 1x is available:

Only the MSM8655 processor has a 1x band, so the session can be either data or voice, but not both. Even if the MDM9600 had 1x, it would not be possible to have simultaneous 1x voice and data because it is impossible to squeeze a 1x band into another 1x band.​

Droid Charge, LG Revolution, and other current Verizon 4G phones: The phones all share the fact that their 4G radio only supports 4G, there is no 3G or 1x data band in the second radio like the MDM9600 used in the Thunderbolt.

In the case of the LG Revolution, the same MSM8655 used in the Thunderbolt gives the phone its processor, and in this case, its 3G and 1x bands (The 3G is enabled on the MSM8655 on the Revolution but not on the Thunderbolt). This is because its second radio, the LG L2000, is only capable of 4G LTE.

In the case of the Droid Charge, the Hummingbird processor used does not have a built in radio. While the Thunderbolt and LG Revolution use a (Processor + Radio) + Radio methodology, the Samsung Droid Charge uses a Processor + Radio + Radio method. The Droid Charge has a VIA CBP7.1 radio to handle 3G and 1x, as well as Samsung's own CMC220 radio that once again, is only capable of 4G.

This results in the Revolution and the Charge behaving the exact same way:

When in a 4G LTE zone:

The phone's 4G radio handles data, while the phones primary radio handles voice.​

When only 3G is available:

On both phones, the 3G / 1x radios do not support SVDO. Therefore, the phone can support a single 3G data session until a call is placed, in which case the phone drops to 1x voice, removing data access while in the call.​

When only 1x is available:

Same as when only 3G is available, except the phone is holding a 1x data session until a call is placed, in which case it becomes a 1x voice session, removing data access while in the call.​

As for current 3G phones, no singular chipset fully supports SVDO, and since almost all phones only have one 3G/1x radio, simultaneous voice and data on these phones is impossible.

SVDO requires the carrier to support the technology, as well as the chipset in the phone to support it and the software to enable it. So far, no individual chipset supports SVDO. This includes the MSM8655, otherwise the LG Revolution would support SVDO over the 3G/1x bands built into the processor. But it does not. This first gen hardware is hacked together as 3G phones with additional 4G radios. This allows the Thunderbolt to get SVDO simply because its 4G radio also supports 3G. Since the software is written to allow SVDO, the two radios work together to provide it.

Late next year I would expect to start seeing matured single-chip solutions containing 4G + 3G / 1x in a single chip. These chips should allow built-in SVDO + VoLTE. Until then, there's not much support for it in current hardware without a multi-chip solution.

Lastly, I'm sorry for the long, drawn out, entirely off-topic post. But I hope it clears up some thoughts as to where we are headed with current CDMA technology and the transition to LTE.