I’m hearing a lot of podcast ads for the prepaid phone carriers (used to be heavily Ting, now it’s heavily Mint), and I’m considering flipping from T-Mobile to one of them.
Does anybody here use a prepaid carrier for a phone line that actually makes / receives a bunch of calls? Any helpful experiences to share, particularly with call quality and customer service?
You’re talking about MVNOs which buy access wholesale from big networks and resell to consumers. Mint does this with T-Mobile and they offer a good deal for the price - call quality should be fine, but customer service will necessarily be variable.
The cheapest MVNO that piggybacks off T-Mobile’s service is Tello.
If you’re happy with T-Mobile service they run two MVNOs themselves: Boost and Metro. (AT&T owns Cricket, and Verizon owns Visible.) If you’re concerned about customer service those are probably the best bets.
(I’ve been using T-Mobile for years in NYC and it’s fantastic here. Paying around $80/month for one line with unlimited everything plus included iPhone hotspot. Not cheap but for me ultimately worth it.)
I’m looking at the different prepaid options, because right now I’m paying about $100 to T-Mobile for iPhone + iPad with cellular. I’m thinking of dropping the iPad cellular and relying on iPhone tethering on the rare occasions when I need cellular for the iPad.
But I’m also considering switching the phone to a prepaid service. The thing is, this is a business phone - so the phone calls aspect of things needs to work. I use very, very little data in practice (less than a gigabyte per month most months), as my data usage habits were pretty much formed back in the days when data plans were expensive, and during the years when I had Ting. 
So that’s the sine qua non for me - reliable voice service. If I can get that on a prepaid line, I can save a rather large amount of money. But it needs to work, and I need to be able to get somebody on the phone when it doesn’t work to fix it.
If that were your situation, what would you do?
Bottom line for voice calls I’d personally stick to major carriers. MVNOs might be fine, but I don’t have personal experience and I don’t know if there any little gotchas, like possible sound compression to save data on voice calls. (Not saying there is, just that’s something I’d look into doing were I running an MVNO.)
When I looked into an MVNO for a relative I noticed that none at the time offered unlimited hotspot. So you could at least save money by keeping your phone plan but dropping the IPad plan in favor of using it with the iPhone hotspot.
You should also note that MVNOs often can’t do addons like iPad or Apple Watch.
I currently use mint for my ipad but it is a full cellular plan at $20/mo.
I’m on Comcast’s MVNO because (at least as of a year ago) it is the only one that can do an Apple Watch data plan. It’s fine but it has a big weak area in my city that Verizon, its network, doesn’t. $45 for unlimited everything + $10 for the watch.
I used Metro PCS before I switched to TMobile, and they were just fine. We only switched because I had Netflix rolled in with a Military Plan
Basically the same call quality, signal coverage, all of that? That’s what I’m really worried about. As long as my phone rings and can ring others reliably, I’m good. 
I wonder if that’s because Verizon has access tiers, or because Verizon has roaming agreements that may not apply to their MVNO clients?
I found that to be the case with T-Mobile. I remember looking at Mint back in the day, and their caveat was limited roaming. I may have read it wrong, so double check. I think Metro is rebranded as Metro by T-Mobile right? The MVNO stuff limits you during traffic overload, and here in Northwest Ohio, I didn’t find my traffic overload lol.
I suspect the latter in this case because it is so consistent. It’s a bit surprising because Comcast is probably big enough to negotiate different rules than other MVNOs. The local xfinity store is actually in the weak area so they should know about it, too!
That’s always hilarious when that happens. You’d think they could at least put their stores someplace where their customers would have service.