Disclosure: I've worked for Consumer Cellular in the past, and my wife currently works there.
It's really too bad that, in general, people only give negative reviews, when they are a small minority. Whether it's specific sites like this one, Facebook, Yelp, etc. it is a known fact that if someone has a negative experience, there is a very high likelihood that they will post a negative review (even though those cases are relatively rare.) Whereas if someone has a positive experience, or are indifferent, they will rarely write a review.
So I'm going to take my time and clear up some of the issues brought up in these reviews:
"Unlimited"
The graphic above clearly shows what Unlimited services Consumer Cellular offers: Unlimited Talk ($20 a month) and Unlimited Text with ANY Data Plan; minimum of $5 a month.) So, for $25 a month, you can get Unlimited Talk and Text (if you don't plan on using Data, and are getting a smartphone, I would encourage you to have them disable the Data feature on your account.) A further point, nowhere do they pretend to offer Unlimited Data.) On the off chance you think the above graphic is made up, here's a link to their plans:
https://www.consumercellular.com/Plans
I can't speak to the supposed damaged phone issue and their refusal to accept its return, but this is not a shady company. They are not going to damage a phone, just to say it can't be returned. I personally know people in the returns department. There is no motivation for this. Chances are, the customer damaged the phone themselves.
"screwed up... coverage... T-Mobile"
Without any real solid technical info to go on, all I can do is make an educated guess as to what happened. It sounds like the customer had an iPhone with T-Mobile. They switched to CCell (transferring their phone number, called Porting in cell phone industry parlance,) and it didn't work. There are numerous reasons how this could have happened. The most common reason is the Port didn't go through automatically. Telecom companies don't want to lose customers, so when a customer switches from one service provider to another (and wants to keep their phone number,) the former company often drags their feet releasing the phone number. If the former account is in good standing (not behind on their bill, out of contract period, etc.) then it should be as simple as having someone at the latter company (in this case CCell,) "Push" the Port through. My wife and I actually had to do this when we switched from Qwest to CCell.) It's not uncommon. The other possibility is that the customer was still under contract with T-Mobile and so their phone was Locked, and that's why they didn't have service. That's pretty unlikely, since part of the questioning for Customer Service Reps is specifically asking about that.
"Signal Coverage"
This one is pretty simple and straightforward: Check out the coverage maps for AT&T and T-Mobile (which I will list below.) Smartphones are actually notorious for poorer cell signal strength in certain circumstances (inside buildings with primarily brick or metal materials, etc.) I didn't believe this until I started experiencing it for myself. It's interesting to me that smartphones aren't designed with a retractable antenna. I know that sounds stupid, but I'm surprised at how much of a difference that can make. Back when we were with Qwest, I had a flip phone with a retractable antenna. Qwest used Sprint towers. At the time, my dad and his then wife lived in a small town off Highway 126 at the base of the Cascade Mountain Range. Basically no carrier had coverage there ((they still don't) combination of being too far outside the coverage area of Eugene, OR and the physical geography of the mountains interfering with cell towers in general.) But that specific phone had coverage. (I later bought a bar-style phone that did not.) At the time, I joked about how I could probably get a signal from an underground bunker. As far as CCell goes, when it comes to coverage, it's within the top four carriers (again, as stated in the article.) It covers roughly 99% of the country. If you're not within the coverage area of Verizon, AT&T, Sprint or T-Mobile, then consider yourself a part of the 1%. And maybe look into getting a satellite phone.
AT&T Coverage Map:
https://www.att.com/maps/wireless-coverage.html
T-Mobile Coverage Map:
https://www.t-mobile.com/coverage/coverage-map?icid=WMM_TMNG_Q317NETWOR_U93HOR6MPAX9955
Conclusion:
Don't pay attention to customer reviews. Especially when a company or product is highly regarded by a reputable site (such as this.) More often than not, it's a knee-jerk reaction to a negative experience (which are rare, and in most cases can be fully resolved if the customer is patient and willing to actually communicate.) CCell has many (millions) of satisfied customers. If just 1% took the time to write reviews, sites like this would be flooded. They have received top awards from Consumer Reports for several years, as well as top awards from J.D. Power and Associates for a handful of years.
https://en.wikipedia.org/wiki/Consumer_Cellular#cite_note-WABC2010-6
Read for yourself? Yeah. And you will find out this is a great cell phone provider.