I have an EC-20 and was never able to get it run reliably on ATT even though the card specs met the carrier specs.
My analysis attached is a year old, so not sure what has changed. I show ATT and T-Mobile on GSM and Verizon and Sprint on CDMA, but not sure this is correct, at least now. CDMA is 3G tech. I think they are all on 4g tech. My ATT iPhone indicator says either ATT or LTE on it, so I assume it’s switching tech depending on location.
The EC-25 overall card specs show 3g as WCDMA and 2 types of 4g, with only FDD-LTE supported on the relevant (US Market) -A and -V cards.
All this means little. What we have not discussed is “Bands” and “Frequencies” (about half way down my document - again a year old).
Sprint and Verizon use totally different LTE bands (25,26,41) vs (2,4,13)and mostly different frequencies so the -V will probably not work for Sprint and there does not appear to be a product solution from the vendor for B25.
That said the EC25-A does meet the specs for both AT&T and T-Mobile. It also looks like Verizon should work too. This gives me concern about either or both my year old data or overall general compatibility. It’s probably worth validating the various carriers direction for their primary bands. the EC25-V spec would indicate my info is incorrect.
I do not know what is meant by verified, though interpret this to be they have qualified it through actual testing and can tell one the proper parameters to make it work. When I activated my EC-20 at ATT they checked the IEME number and knew what type of board it was and the vendor, but they were not able to help be configure it.
NOTE: not stated in my file is that each carrier has multiple bands and frequencies, but not all in all locations. the first is the primary band or frequency and the direction for new installations or upgrades (worth validating). The others are a result of acquisition. You will probably not find any information of which bands are served in which locations.
I think that the solution is to field test the cards and that if it does not work off the bat try the config in multiple locations (towers).
The Sierra wireless cards are about 4x the price in general, but it seems there is a good price on Amazon for the 7355 card, but you only get the B25 band. Looks like the 7455 will work for all but is close to $200
https://www.amazon.com/Sierra-Gobi5000-EM7355-Thinkpad-04W3801/dp/B00JL7PDOG