It depends where you are. I recently finally got tired of Sprint's bullshit (like charging me a $10 "4G" fee because my phone was WiMax - i.e. has never, ever worked as a 4G phone) and switched to T-Mobile. It works pretty well around home and the office, but it has a lot of spotty coverage in the "in between" areas, and none at all at the SO's apartment. Wifi calling didn't work right there, either, probably because of having 20+ SSIDs pumping through her living room. So coverage can still be a very real concern for them.
OTOH, they seem to have the self-awareness to realize this: When I called them about the problem, they hooked me up with a "free loan" (i.e. I have to send it back if I change carriers) of a 5gHz WAP. Hopefully that nails down the problem, but it's sure a nice surprise either way.