I am just wondering what the sunset date is for the AT&T 3G cells.
There has not been any official sunset date confirmed yet afaik for machine to machine comms using HSPA.
I believe the expected sunset for 3G voice/data is December 2021, but I don’t believe that is official, just an “it will at least be supported through then.” Note that timing and decisions that affect voice and data activation through the network do not necessarily correlate with machine to machine service contracts.