Yealink SIP-T48G Administrator's Manual page 265

Press the OK key when the IP phone is idle to check the firmware version. For example:
7.7.0.50.
Item
1
2
3
4 50
A unique digit used to identify the phone model.
The unique digit for each IP phone model is:
7
35: SIP-T48G

7: SIP-T22(P)

Firmware generation.
7 Note: The larger it is, the newer the firmware
generation is.
0 A fixed number.
Firmware version.
Note: With the same firmware generation, the
larger it is, the newer the firmware version is.
Description
Troubleshooting
253