Yealink SIP-T54S Administrator's Manual page 927

The following figure shows the Flash event sent by the IP phone when transmitting DTMF digit
using the RFC 2833 DTMF type:
Procedure
Configuration changes can be performed using the configuration files.
Central Provisioning
(Configuration File)
Details of Configuration Parameter:
features.dtmf.dtmf_flash
Description:
Enables or disables the IP phone to send Event Flash by transforming the letter E.
0-Disabled
Event encoding (decimal)
0-9 0-9
*
#
A-D 12-15
Flash
<y0000000000xx>.cfg
Parameter
Configuring Audio Features
10
11
16
Configure DTMF send event flash
feature.
Parameter:
features.dtmf.dtmf_flash
Permitted Values
0 or 1
Default
0
901