The Yealink T48 phones have the ability to add a USB WiFi dongle that will allow the phones to connect wirelessly over WiFi.  Great for applications where no CAT5 data wire exists.

Set up and plug in your phone, once the phone is completely powered up, Insert the USB Module into the back of the phone receptacle.

You will get a pop-up asking 

"WiFi adapter is added, scanning available wireless networks right now?"

Click "OK"

This will take you to the WiFi screen, 

after scanning it will display several WiFi networks,

Click on the one that is yours.

This will open the password screen, 

use the on-screen keyboard to enter your password, 

hit the return key when finished.

(For numbers and symbols, click the "&123" button on the lower-left hand side)

This should take back to the previous screen where it should say connecting, 

and then "Connect successfully!"

You are now connected and can press the house symbol in the bottom right corner to return to the home screen.