Question about Yealink T48g

It is possible. You need Yealink WLAN Adapter WF40 Yealink WLAN Adapter WF40 . Here are the instructions https://www.youtube.com/watch how to configure it. The first important step is to update the firmware of the phone because the older firmware versions did not have Wi-Fi functionality.

There is also a Bluetooth adapter Yealink Bluetooth Adapter that allows you to connect the phone to Bluetooth headsets.

Unfortunately, T48G has only one USB slot. So you can't have both Bluetooth and Wi-Fi at the same time.

Some of the newer Yealink 5 generation models have both Bluetooth and Wi-Fi (2.4 GHz) built in.

Like for example with:
Yealink SIP-T56A Yealink SIP-T56A or
Yealink SIP-T58A Yealink SIP-T58A

They are not much more expensive than T48G. If you need Bluetooth and/or Wi-Fi, they might be a better choice than T48G.

As already answered, the phone can be connected to WiFi, but only with the WiFi adapter WF40.
Otherwise, I can only warmly recommend this phone.