[General Questions and Answers] IT_Architect:
This is what I've summarized based on what I've learned.

U.S. lay of the land:

- AT&T is the GSM network in the U.S. most likely to be able to service you satisfactorily.

- AT&T as a rule does not work with carrier unlocked U.S. or international phones from a practical standpoint. Even IF you manage to get it to work somewhat with their network, you will have at least these service issues:

1) AT&T will not do carrier aggregation therefore maximum download is around 17mbps and upload is around 6mbps while with an AT&T branded phone download is 82mbps and upload is 44mbps.

2) AT&T will not provision LTE advanced features such as VoLTE, Wi-Fi calling, or advanced messaging.

3) AT&T will not recognize the IMEI in order to push secondary LTE bands which in turn also throttles bandwidth.

- AT&T works grudgingly, with T-Mobile phones. Government edict forced them support B12 as well as their B17 (a subset of B12) to be interoperable with T-Mobile. If you go with the T-Mobile phone to pickup the new B71 600 band, you lose out on the AT&T B17 range of B12, which is well managed by AT&T.

- The U.S. Unlocked Note 9 SM-N960UZBAXAA (128GB) is the best of all worlds. It has the SnapDragon, all of the AT&T bands and T-Mobile bands for the current and foreseeable future, AND all of the Colombian band for the current and foreseeable future, AND all of the CDMA bands for Verizon and Sprint. It is in most cases less expensive than the carrier versions. The problem, as mentioned, is getting it to work well with AT&T. I would guess the same situation exists with other carriers as well, and that it would require legislation, like they did with cable companies, to change that.

Summary:

- I need to pick an AT&T branded phone, and get it unlocked in order to work in the U.S.

- The phone needs to be able to also do the Colombian bands.

Colombian Bands

GSM (2G) 850, 1900 (PCS) - Claro, Movistar, Tigo

UMTS (3G) B2 (1900 PCS) - Claro, Tigo

UMTS (3G) B4 (1700/2100 AWS 1) - Movistar

LTE (4G): Band 2/1900 - Movistar

LTE (4G): B4 (1700/2100 AWS 1) - Movistar, Tigo

LTE (4G): B7 (2600) - Claro, Tigo

LTE (4G): Band 38/2600 - DirectTV data

LTE (4G): Future - Colombia will "real soon" (when pigs fly) be auctioning in the 700 range 2x 15MHz blocks (Block A/B12), 2x 10MHz blocks (Block B/B12) and two 2x 5MHz blocks (Blocks C/B12&orB13, and D/B14). A supplementary 2x 2.5MHz block of 1900MHz spectrum will also be auctioned, comprising frequencies in the 1865MHz-1867.5MHz/1945MHz-1947.5MHz bands (Block E/B25).

AT&T Bands

https://www.frequencycheck.com/carriers/at-t-united-states

GSM Supported Protocols: GPRS, EDGE

GSM (2G) 850, 1900 (PCS)

UMTS Supported Protocols: UMTS, HSDPA, HSUPA, HSPA+

UMTS (3G) B2 (1900 PCS), B5 (850)

LTE Supported Protocols: LTE, LTE-A

LTE (4G) B2 (1900 PCS), B4 (1700/2100 AWS 1), B5 (850 CLR), B12 (700 abc), B14 (700 public safety), B17 (700 bc), B30 (2300 WCS), B40 (TDD 2300 implementing), B66 (1700 AWS)

Note 4 N910A (AT&T) - Note 4, by far my favorite, and Note 5 fail because they do not support Movistar's UMTS (3G) B4[/B]

https://www.frequencycheck.com/models/GLDb7/samsung-sm-n910a-galaxy-note-4-lte-a-samsung-muscat

GSM Supported Protocols GPRS, EDGE

GSM (2G) 850, 900 (E-GSM), 1800 (DCS), 1900 (PCS)

UMTS Supported Protocols UMTS, HSDPA, HSUPA, HSPA+

UMTS (3G) B1 (2100), B2 (1900 PCS), B5 (850), B8 (900 GSM)

LTE (4G) B2 (1900 PCS), B4 (1700/2100 AWS 1), B5 (850), B7 (2600), B12 (700 abc), B17 (700 bc), B29 (700 de),

Supported LTE Protocols LTE, LTE-A

Note 8 N950U (AT&T) - Note 8 & 9 support all bands for all three Colombian carriers current, and the proposed bands

*Differences between Note 8 and Note 4 are highlighted in red.

Note 9 adds B66/AWS-3 which is used by U.S. T-Mobile's 4G, but not T-Mobile's new B71 (600) that they are rapidly deploying. That is only available on the T-Mobile model.

*Differences between Note 9 and Note 4 and 8 are highlighted in blue.

https://www.frequencycheck.com/mode...axy-note-8-td-lte-us-sm-n950u1-samsung-baikal

https://www.techwalls.com/samsung-galaxy-note-8-sm-n950-model-number-differences/

GSM Supported Protocols GPRS, EDGE

GSM (2G) 850, 900 (E-GSM), 1800 (DCS), 1900 (PCS)

UMTS Supported Protocols UMTS, HSDPA, HSUPA, HSPA+

UMTS (3G) B1 (2100), B2 (1900 PCS), B4 (1700/2100 AWS 1), B5 (850), B8 (900 GSM)

TD-SCDMA (3G): B34(2010), B39(1880)

LTE Supported Protocols LTE, LTE-A

LTE (4G) B1 (2100), B2 (1900 PCS), B3 (1800 +), B4 (1700/2100 AWS 1), B5 (850), B7 (2600), B8 (900), B12 (700 ac), B13 (700 c), B17 (700 bc), B18 (800 Lower), B20 (800 DD), B25 (1900 +), B26 (850 +), B28 (700 APT), B29 (700 de), B30 (2300 WCS), B38 (TD 2600), B39 (TD 1900 +), B40 (TD 2300), B41 (TD 2500), B66/AWS-3

Summary

I can come up with other phones that will straddle the fence, and some are quite inexpensive. However, if I want a Note, I can't go less than the Note 8 to do it.

Thanks for all of your help!