After a couple of months with it, agreed on all of the above. Also iPhone is a poorer choice than Andoid in that TMo is working on lighting up their 700 MHz spectrum in some areas and iPhone doesn't have the band. Not even the 6/6+. Not that many Androids do either but if you're going for max coverage on their network, get the latest phones with the "new" band.
Tech wise they simply can't compete with VZ. They don't have the bandwidth. They probably bid on a lot of it in the recent AWS auction but it'll be a while until that comes online and of all things, Dish Network just snapped up a crap-ton of that auction and no one is quite sure just why yet.
- Coverage in DEN is good. Typically 10x10 which gives about 20 Mb/sec LTE.
-VoLTE issues: There are gaps between some LTE towers and iPhone is defaulted to VoLTE so calls sometimes drop. They do not have their LTE to lower tech handoffs working. Forcing the phone to use LTE only for data and not voice can help on this regard if you're regularly in gappy LTE coverage areas. I'm not so I leave VoLTE on for the HD audio when calling TMo VoLTE to TMo VoLTE which is 70%+ of my calling. If I know I really need a call not to drop I'll go into settings and kill VoLTE.
- Coverage at my house is nonexistent but they maintain a roaming agreement with Viaero/Cellular One of NE Colorado. iPhone gets confused for a minute or two on my commute trying to decide if it should hold on to TMo's network or switch. One can also play games with forcing a carrier in the settings screen but it takes just as long as waiting it out.
- When roaming you'll get almost no data speed but voice will work flawlessly. Text also. But... And this is a big but for iPhone users...
- Spotty data means spotty iMessage. iMessage uses data not SMS. So expect weirdness with iMessage. I don't care but it'll drive some crazy in spotty coverage that they can get a standard SMS message but not messages from other iPhone users.
- Coverage in LNK was virtually nonexistent. It was really bad. Never lost voice/SMS coverage but data was usually useless.
They're most assuredly an "also-ran" carrier. You need to be careful to see if your usage and individuals care levels match okay with their coverage in your area. They do have a try before you buy thing where they'll ship you an iPhone 5C or 5S and let you try it for a week. Highly recommended.
As for me, still happy with it. Works well enough for half the price of VZ that I'll keep it. I'll probably augment it with a VZ based wifi hotspot device at some point when I go traveling just to make sure I have data coverage. Nobody beats VZ on that. AT&T is close but they have some technical challenges in some areas.
One plus to using VZ as a backup unless they're blocking it, and I doubt it... TMo devices will connect to their network and route calls via WiFi. Analyzing the packets, what they're doing is nailing up an IPSEC tunnel on port 4500 outbound to their network and then routing calls to the device over that. At home I poked some QoS rules into my pfSense firewall to give the IP addresses of the iPhones some "guaranteed" bandwidth at all times and so far it's working pretty well. We have good enough actual cell coverage at home to get low speed data and voice just fine so it's not really needed there and I keep VoIP calling off for the most part. I've also routed the Voip thing through network sharing from a Mac running Yosemite at the office (double NAT, once at the Mac, once at our corporate firewall) and it works fine there also.
The IPSec tunnel is NOT smart enough to try an alternate port number if all 4500 traffic is blocked like say, Skype will do, nor masquerade as port 80/443 traffic. Too bad. But it is what it is.
The VoIP connectivity WILL do HD quality audio codecs. Sounds nice. Uses just under 200 Kb/s with overhead.
There ya go. More geek info than you probably wanted.
Oh. VOIP calling also worked on a certain Nebraska tech company's guest Wifi network.
I just happened to have it turned on and it connected.