So Google Fi didn't work out. Even though I had excellent data signal quality, cellular calls were extremely spotty. Often, the other party could hear me just fine, but I couldn't hear anything at all from them. Sometimes, I could hear the other party when calling in one city but not another, even though I had equally good signal quality in both cities. Google's technical support had me perform a factory reset of my phone and they sent me a new SIM card, but that didn't fix the problem.
Also, Google Fi doesn't support visual voicemail of any kind. (I hadn't thought to look into this before I switched.)
So I just switched to Mint Mobile. Cellular calls are crystal-clear, and visual voicemail works.
$15/mo for 3 GB of data.
The funny thing is, Google and Mint both use T-Mobile's network. So it's the same cellular network, but it works better on Mint than on Google. So there's obviously something wrong with Google.
Also, Rick Moranis!