Verizon and AT&T may not be able to rival a big T-Mobile 5G breakthrough anytime soon

In response to that truly groundbreaking August 2020 move, all AT&T and Verizon could muster were vague promises of similar rollouts of their own taking place sometime "soon" and unconvincing assurances that development work and "core" tests were well underway. Unfortunately, nothing much has changed since then on the standalone (SA) 5G launch front, at least as far as actual consumers are concerned, and if anything, the two carriers' renewed promises and statements feel even less encouraging than before.
No timelines to announce at the moment
Ronan Dunne, Big Red's executive vice president and Consumer Group CEO, essentially said as much at a FierceWireless event this week, highlighting his company's short-term focus on "prepping the network for C-band's arrival" over a standalone core deployment, which is "absolutely" on the roadmap, but unlikely to happen very soon.

Verizon is making plenty of promises, but nothing concrete regarding standalone 5G
Reading between the lines of Dunne's statement, we can't help but assume Verizon will give full "priority" to its C-band preparation work in 2021 while shelving any and all 5G standalone rollouts until 2022.
AT&T looks similarly committed to... dodging questions about specific 5G SA launch schedules, vowing to unveil "those timelines in due course" and waxing poetic on the "journey of going fully scalable nationwide" following the many tests already taking place across a lot of regions. Meanwhile, T-Mo's top execs must be brimming with pride looking at Magenta's dominant 5G availability numbers, achieved in part thanks to standalone technology.
What is 5G SA and why is it important?
Because it's a little easier to explain, let's start with the "why" of the equation. In a nutshell, standalone 5G is expected to improve everything from network latency to download speeds, and of course, coverage with no need to free up and deploy any additional spectrum.
In Verizon and AT&T's defense, this is a decidedly forward-thinking technology widely predicted to change the game further down the line, at which point the two "traditional" carriers may well catch up to the industry-disrupting "Un-carrier." In contrast, the aforementioned C-band rollouts have to happen ASAP for Big Red and Ma Bell to close the gap to Magenta's towering balance between 5G Ultra Capacity speeds and availability.
In terms of what it all means, 5G SA basically leaves 4G LTE connectivity behind altogether, exclusively using 5G cells for both signalling and information transfer and thus bringing 5G "closer to reaching its true potential" by paving the way for entirely new applications and "supercharging things like mobile augmented and virtual reality, cloud gaming, real-time translation and so much more", according to T-Mobile.
Non-standalone 5G, meanwhile, still keeps existing 4G LTE networks in play for control functions, which can simultaneously impact the efficiency, performance, and coverage of a carrier's 4G and 5G signals.