[Android Q&A, Help & Troubleshooting] reb00tz:
Hi, just to share results of my research on dual-SIM, simultaneous 4G/3G capable phones.

Do note that there are confusing and ofttimes purposely misleading terms; there are differences between:

the use of FDD-LTE vs. TD-LTE (sometimes misleadingly referred to as "dual LTE")

the ability to switch the "primary SIM/slot" (which has LTE/4G+/4G/3.5G/3G capabilities) with the second/secondary slot without physically swapping the SIM cards (refer to misleading/misinformed information within the OneNote notebook as linked, from no less than one of Singapore's

leading

telcos)

the ability to

simultaneously

maintain a 4G/3G connection on

both

SIMs

Before we start seeing responses in this thread from people asking:

why would you need 2nd SIM to be on 3G at the same time?

simply because there are countries that:

will be shutting down their 2G networks (e.g. US, AU, SG)

have service providers that do not run 2G (i.e. GSM) networks at all (e.g. CA, JP, KR)

why would you need two data connections?

There is a difference between: data connections and voice connections over 3G; if your phone is currently on LTE/4G+/4G and both your handset or your service provider/current service cell tower is not VOLTE-capable, make a phone call and you will note the connection "drops" to 3G (voice).

(caveat: there may be some people that want dual/separate data paths for different apps, but I believe those to be in the minority and not the target/purpose of my research)

The "crop" of "current" generation dual-SIM capable phones in wide-spread markets from the "big guns" (e.g. LG G5, Samsung Galaxy S7 and A 2016-series) cover points #1 and #2, but fail on point #3.

Legend:

highlighted in green background: arguably best in class

highlighted in red background with white text: arguably worst in class (or does not meet the needs of this article; i.e. "4G + 2G only")

red text: warning/of detrimental note

"question marked": unsure/unchecked

For the bands and the countries, that is for my internal reference only, covering most of the countries of my concern; please use that as a guide; I will not entertain requests to add more countries (as it will be a herculean/endless task).

Do note the table is

incomplete

(those with question marks); particularly I stopped bothering about other aspects if I confirmed it was not simultaneous 4G/3G capable. If you know of any other simultaneous 4G/3G-capable phones, please let me know to add them, but please stick to "current" phones (i.e. announced/released from 2015 or preferably mid-2015 onwards) and please also provide at least two other "official" references confirming said capability (and please do not use two "sources" that circularly-reference each other or the same "source").

NOTE: I have not stated nor verified VOLTE, either on SIM #1 or switchable primary, which is another point of interest for me; if you have any information, please let me know as well.

Thanks!

P.S.: Whereas I have seen quite a few direct edits, corrections and contributions, someone (eventually) deleted the entire page. It has been restored but made read-only for now; please PM me and I will provide an editable link.

Meanwhile, until someone else finds a better way, or I find the 2+ hours needed to properly tabulate it (i.e. put it into an easier-to-read table), consider this version "stale" from herein.