Yealink T48S Phones Failing to Provision/Reprovision with Zoom Phone

Try these 2 steps: 

1. Make sure device access to Yealink RPS server isn’t blocked on firewall. Then perform a factory reset.  Server and port details can be found in https://support.yealink.com/docs/yealink-management-cloud-service-ymcs/network-requirements/3a94e8bc2689402bb801d0cc613e9230
2. After factory reset is complete, log into the device web interface as admin, navigate to Security - Server Certificate - Device Certificates selection, change from "Custom Certificates" selection to "Default Certificates". Save the change and try provision it again. 

hi ​@Fonzie78 

According to Zoom Phone Certified Hardware, Yealink T48S desk phones manufactured before 2019 are not compatible with Zoom Phone.  “ Note (C): Yealink devices manufactured before 2019 are not compatible with Zoom Phone encryption and certificate security requirements. The device will fail Zoom Phone provisioning, even if it was added to the account manually or in bulk.”

You can check the date the T48S was manufactured by following the Zoom Phone Certified Hardware procedure:

Check the manufacturing date of a Yealink phone

Some models of Yealink devices manufactured before 2019 will not be compatible with Zoom. By following these steps, you can easily determine the manufacturing date of your Yealink phone.

1. Locate the serial number. You can find the serial number on the label, box, or within the user interface of the device.
2. Determine the manufacturing year:
   • For phones manufactured before or during 2021:
     1. Look at the 6th and 7th digits of the serial number. These two digits represent the last two digits of the manufacturing year.
     2. For example, for the serial number 312921805020XXXX, the 6th and 7th digits are 18, indicating the phone was manufactured in 2018.
   • For phones manufactured in 2021 or later:
     1. Look for a letter in the serial number. This letter represents the manufacturing year.
     2. For example, for the serial number 808040D04000XXXX, the letter D indicates the phone was manufactured in 2021.
        • D stands for 2021. E stands for 2022. F stands for 2023. G stands for 2024.

In addition, Yealink phones used with Zoom Phone must use custom firmware designed for use with Zoom Phone.

Yealink custom firmware required

Yealink phone models require a custom firmware that is built specifically for Zoom Phone, while certified IP phones from other manufacturers use the firmware that comes from those vendors and isn't specific to Zoom Phone.

As of 10/12/2026, the Yealink firmware for T48S use on Zoom Phone is: 66.85.3.23.  This firmware can be downloaded from Zoom Phone Certified Hardware using the link next to T48S.

If Zero Touch Provisioning (ZTP) is not working for you, you can use assisted provisioning. Please see Getting started with provisioning desk phones.

Please let me know if this information solves your issue or if you need additional help.

Thanks,  eliot

Thank you for taking the time to respond. I really appreciate the suggestions.

We did look into the manufacturing dates early on and confirmed that our T48S phones were manufactured in 2019. We also checked with Zoom Support, who confirmed that these phones should still be compatible.

We've tried several firmware versions at the recommendation of both Zoom and Yealink, including downgrading to 66.85.3.21 and then upgrading back to 66.85.3.23, but unfortunately, we're still seeing the same issue.

The strange part is that these phones work perfectly fine until we attempt to reassign them to another user. Once we do that, they simply won't provision again. We've been able to reproduce this on multiple phones, even when connected directly to the internet, so we've ruled out our internal network as a possible cause.

We're continuing to work with both Zoom and Yealink Support and have provided extensive logs and packet captures, but so far we haven't been able to identify the cause.

Thanks again for your input. It's greatly appreciated, and I'm hoping someone who has experienced something similar might be able to shed some light on this.