I managed to do some sleuthing, and it appears that the 2018 Clarity actually does have a 4G LTE (as opposed to 3G-only) cellular module! First, I found that the model number of the TCU used in the 2017-2019 Clarity is 39770-TRW-A51. From there, I found a photograph of one of these units including its label, one of the items on which says: "Contains FCC ID RI7LE920NA1" Looking up FCC ID RI7LE920NA1 reveals that this module is a 3G and 4G LTE compatible cellular module, capable of supporting LTE bands 2, 4, 5, 7, and 17. This is great news, as it means we shouldn't be affected by the upcoming AT&T 3G sunset!
Nice. At some point I checked with Honda and they told me not to worry, but couldn't provide any details. I just looked (there's an ebay for that part), and it does look like many of the AT&T LTE bands are covered.
