Core Issue
The Cisco Analog Telephone Adaptor (ATA) 186 has a cached value of its profile stored in the Flash ROM. This is what you either see or hear through the web server interface or Interactive Voice Response (IVR).
If the USETFTP parameter is set to 1, the cached value of the ATA 186 profile is synchronized with the profile located on the TFTP server. This synchronization update of the cache value happens approximately at the interval determined by the CFGINTERVAL parameter's value or at power up reset.
Resolution
If you are using TFTP for provisioning, you should not be using the web server interface or IVR to modify the value of your Cisco ATA's profile. The web server interface or IVR should only be used when first configuring the Cisco ATA to use TFTP provisioning. If you are not using a TFTP to provision your Cisco ATA and are using the web server interface or IVR to configure the Cisco ATA profile, the USETFTP parameter should be set to 0.
For more information, refer to these documents:
Frequency and Scope of Symptom
Occurs at regular intervals
Voice Gateways
Non-IOS gateways
ATA 186
