You mean there is Lumia supporting LTE for both SIM slots simultaneously? Actually I have never seen that on any phone before.

As of LTE-capable DualSIM Android phones, I'm using the Samsung Galaxy S5 DuoS (SM-G900FD) which however does only support American LTE frequencies highlighted below: 800/850/900/1800/1900/2100/2600
As the 850MHz band (LTE band 5) is only used by US Cellular in some regions, there are only few 1900MHz networks left that would be compatible.

Despite there are numerous LTE-capbale DualSIM phones I fear the choice for Americans is very limited as most phones are designed for Asia and Europe and hence lack frequency band support for most of the Americas.

You mean there is Lumia supporting LTE for both SIM slots simultaneously? Actually I have never seen that on any phone before.

As of LTE-capable DualSIM Android phones, I'm using the Samsung Galaxy S5 DuoS (SM-G900FD) which however does only support American LTE frequencies highlighted below: 800/850/900/1800/1900/2100/2600
As the 850MHz band (LTE band 5) is only used by US Cellular in some regions, there are only few 1900MHz networks left that would be compatible.

Despite there are numerous LTE-capbale DualSIM phones I fear the choice for Americans is very limited as most phones are designed for Asia and Europe and hence lack frequency band support for most of the Americas.

I have no idea whether the Lumia had two idependent radios are some standby scheme. I didn't buy it. Expansys was liquidating at bunch at under $US 200 and the LTA support was interesting because it had a much larger than normal amount of LTE bands.

Hi.
I think there is some misunderstanding here.

Having 3G or 4G/LTE access on both SIM slots means that you can change SIM1 to SIM2 as the 'fast' slot. This becomes more and more standard in the business now. You don't have to change SIM cards from slot to slot, but can do this by software.

But this is different from dual-SIM stand-by and dual-SIM full active. Dual SIM stand-by phones have only one receiver and your phone calls on SIM2 often don't come through, if you are using SIM1 at the same time.

As a matter of fact, there are a few Android phones with dual-SIM active on the market meaning two full radio units built in, but only available from Huawei and Asus so far.
Most of them are in the high-end segment and only in certain versions:
- from Huawei: Honor 8 (FRD-AL00) and Honor V8 (no LTE band 20!) and P9, Mate S and Mate 8 (with LTE band 20).
- from Asus: Zenfone 2 (cheapest of them, again without band 20!) - Here is an example of dual-SIM full active: https://www.asus.com/zentalk/in/thread-8926-1-1.html

So there are some very expensive phones on the market with fully active 2 radios built in.
I personally don't consider this as essential, but the fact that many countries will switch off the 2G eventually (US, Singapore, etc.) So a 3G support of the 2nd SIM should be more important for the future.

By the way there are a couple of phones available now that support 4G or 3G on the primary SIM slot and 3G on the secondary SIM slot simultaneously. For instance the OnePlus 3 does so which I've been owning for more than two months now. But despite this improved capability it is dual stand-by only which indeed means that I cannot receive calls on the other SIM while I'm having a phone call.
There's a corresponding thread on XDA devs: http://forum.xda-developers.com/andr...pable-t3370632