Wireless coverage maps - what does "partner" mean when all 3 networks say that's who is providing coverage for the same area?

I was trying to see which wireless network would work best at a fairly remote place I like to go. When I went to each carrier’s coverage map, two of the three US networks (ATT and T-Mobile) say coverage in that area is provided by “partners,” and the third network (Verizon) says they offer no coverage at all.

Question: If there are only 3 actual wireless networks and one says “no service” while the other two say “coverage provided by a partner,” who’s the partner?

Typing “Northwoods, WA” into the ATT and T-Mobile coverage maps will show you the location in question.

Coverage maps:

Verizon’s map is at verizon dot com /coverage-map
(I’m a new user so I can only put two links in a post.)
On Verizon’s map you have to type “Cougar, WA” and zoom out a little. Northwoods is at the east end of Swift Reservoir, a few miles east of Cougar.

Additional confusing bits:

  • A little bit weird: Verizon’s map clearly shows no coverage, but for the last few years a friend’s Verizon iPhone could often make/receive calls and texts on the lake and showed two bars of LTE but no data would send or receive. Our ATT phones showed no signal anywhere.
  • Much weirder: Last month my daughter’s Consumer Cellular (ATT) iPhone somehow had pretty good service (calls, texts, and often data) on the lake when neither my or my wife’s Consumer Cellular (ATT) iPhones showed any signal, even after restarting our phones, resetting network settings, and asking customer service if they could do something on their end to help (they claimed to have done a mysterious ‘signal boost’ procedure but I’m skeptical).
    My daughter’s phone had a brand new SIM card installed just a few days before, whereas the other two phones SIMs (actual SIMs not eSIMs) are a year old.
    – I’m sure all three phones are on the ATT network.
    – My wife’s phone: iPhone 14 Pro
    – Mine: iPhone 13 Pro
    – My daughter’s: iPhone 12 Pro
    Are the radios and/or antennas in the iPhone 12 better than newer iPhones? Is there some kind of secret sauce in the new SIM?

Thanks in advance for any insights.

I can’t help with IPhones, etc which MAY have the app available, but on Androids you can download an app called Cell Tower Locator. It shows on a map which cell tower you are connected to. At the top of the display it shows who owns the service. There is also technical info such as which frequency band, signal strength, GPS info, etc.

Those aren’t the only US carriers. There’s a wide swath of Wyoming where the best cell service is someone else (Union Wireless). They do sell access to the other companies, but they also sell cell service direct to consumers. There may be a company like that where you’re looking.

Ah-ha! Thank you!
Sheesh, now that you say that I’m kicking myself for not googling “wireless phone companies in Washington” or something before posting here.

Update: I just googled. Seems like Washington is only served by the big 3. I did see that Wyoming has those plus Union Wireless and also one called Viaero Wireless.

Wow, that sounds like a cool app, I just found it on iOS for $3.
Thank you for the tip!