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How to Downgrade Firmware on AudioCodes C435HD Teams Phones
Question details
The user wants to know if it is possible to downgrade the firmware on an AudioCodes C435HD Teams Phone to restore the Hotline automatic dialing feature.
- Product
- AudioCodes C435HD / Microsoft Teams
- Device & OS
- not provided
- Scenario
- Attempting to rollback firmware after recent Microsoft Teams and device updates disabled the Hotline functionality.
- Observed behavior
- The Hotline feature on the phone is no longer functioning, preventing automatic dialing for the organization.
Before attempting any firmware rollback, note down your handset firmware version, Teams client version, and device provisioning method to share with technical support.
Contact Microsoft and AudioCodes Support for an Approved Firmware Rollback
Firmware downgrades on Teams-certified phones require specific administrative access and approved rollback files to prevent bricking the device.
Because firmware rollback availability is strictly dependent on the AudioCodes device model, Teams certification status, management platform, and current firmware policies, users cannot perform a manual downgrade independently. Attempting to install unsupported firmware can cause irreversible damage to the hardware.
To resolve the Hotline issue securely, an Office 365 or Teams administrator must escalate the problem through official support channels.
Gather the affected handset's firmware version, Teams service version, affected configuration details, and export the device's diagnostic logs.
Reach out to your organization's Global Admin, as standard users and forum moderators do not have the required access to backend management resources.
Have the Global Admin log into the Microsoft 365 Admin Center and open a service request with Microsoft Teams technical support to investigate the broken Hotline feature.
Simultaneously, contact your AudioCodes reseller or federated partner for approved firmware rollback files and specific downgrade guidance for the C435HD model.
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Frequently Asked Questions
Why did the Hotline feature stop working on my AudioCodes C435HD phone?
Recent firmware or Microsoft Teams backend updates may have introduced compatibility changes or stricter firmware policies that inadvertently disabled the automatic dialing functionality required by the Hotline feature.
Can I manually install an older firmware version on the C435HD phone?
It is strongly advised against manually installing unsupported or older firmware without vendor supervision. Doing so can void certifications, violate management platform policies, and potentially render the device unusable.
What details are required when opening a Microsoft 365 support ticket for this issue?
You should provide the handset firmware version, the Teams client or service version, the provisioning method used, specifics about the affected Hotline configuration, and backend diagnostic logs from the device privately.
