You may be asking yourself why does my Grandstream show me the wrong weather?
The easy answer is you have to set it.
If you have a single phone, you can simply click on the config button on the weather screen and follow these steps:
1. Down arrow to the city code and right arrow until it shows Self-Defined City Code
2. Down arrow again, to the space to enter the code, click the 3 button on the screen allowing you to pick Alpha, Alpha Numeric and Numeric until you see 123, this will allow you to quickly enter the zip code, then simply type in your zip code and press Save.
You can also change this in the firmware settings which you may find a bit more complex.
Search for the value assined to P1377 and set the zip code there.
Lastly if you are using a PBX such as FreePBX and are utilizing Endpoint Manager, you can do a basefile edit, which will allow you to set each template with the P1377 value thereby configuring many phones in 1 click.
At that point you can tell it to update the configuration, or go all out and update the configuration and apply, which will reboot the phones and force the setting immediately.