Since the T5X was Yealink's latest "cutting edge" they began rolling out other models into that series to fit requirements outside of just Android. Built-in wifi was one such requirement that I expect they had not originally anticipated but due to requests from customers began to build out. This is where the "W" suffix began appearing. So as part of the "W" roll out (which was somewhere between 1-2 years after the initial T5X) you ended up with: The Yealink SIP-T57W supports efficient provisioning and effortless mass deployment with Yealink’s Redirection and Provisioning Service (RPS) and Boot mechanism to help you realize the Zero Touch Provisioning without any complex manual settings.

Yealink doesn't really breakdown/explain their naming concepts, but having dealt with them for many years I can give you a bit of brief history to help clarify things a bit: The way our software determines of the offered firmware is newer than the one on the phone is by comparing all 4 numbers of a firmware version.With the adjustable high-resolution display available on the T57W phone, you can switch angles to your liking and under a variety of lighting conditions. This will ensure an optimized user experience. Enjoy clear calls First phones were TXX series... so T18P, T20P, T22P, T26P, T28P etc. Higher numbers meant more buttons/bigger phone/more features. (if I remember rightly the T18P didn't even have a screen on it). Here, the P actually designated POE support. So they had T22 and T22P versions, one which only worked with power adapter and one which could be power adapter or POE. Eventually as costs of POE circuity dropped the non-poe models went away leaving only the T2xP models.

The T3x were a stop gap measure as they still had the same form factors as the T2x. To keep up with the times, Yealink introduced the more "modern" T4X designs. Since they also originally had 10/100 and Gigabit variants, those models became T4XP or T4XG depending on the switch built into them. In reality the P variant really only hit low end units, and before long the G version was the defacto.For T53W they were aiming for a lower more basic/common use phone that would fit the same form factor/look consistent with the rest of the T5X series. So just like the T41 that's now at the bottom end of the T4X series, you get the original version (T53W) and the "stripped down bare bones" version T53.