For what it's worth, said multi-year undertaking appears to be moving along at a relatively slow but decidedly orderly pace, as T-Mo plans to halt activation of CDMA-only devices and devices lacking VoLTE support on Sprint's legacy network as early as January 1, 2021, according to a recent letter allegedly received by a "valued business customer."
That's a measly four days away at the time of this writing, which feels like exceptionally short notice for something so seemingly important, but that only concerns new activations, so existing Sprint subscribers actually have nothing to worry about... yet.
Then again, their time will come "on or around January 1, 2022" to let go of any and all CDMA-only devices and dual mode CDMA/LTE devices without Voice over LTE capabilities still in use. That's because Magenta intends to completely terminate the archaic Sprint CDMA network roughly a year from now, which seems to more or less line up with the general schedule shared by CEO Mike Sievert just a few weeks back.
Sievert described his company's Sprint-killing moves of 2020 as mostly "isolated" affairs, predicting said efforts will barely begin "in earnest" at some point in 2022. Clearly, a CDMA network shutdown sounds like a big and "earnest" step towards burying Sprint's name and technology altogether after already uniting its brand with that of T-Mobile for marketing purposes and combining the two's 5G resources for, well, Verizon and AT&T-crushing purposes.
Although January 1, 2022 is not exactly right around the corner, it's probably a good idea to look into upgrading or replacing your outdated "equipment" as soon as possible. Something tells us T-Mobile will roll out a number of sweet deals aimed specifically at making your transition from a CDMA-only to a 5G-enabled device as smooth and as cheap as possible within the next 12 months, so be sure to keep an eye out for stuff like that too.