From software 2.37.0 or higher, the option is added to disable the Blind transfer option in the DECT handsets. 

This can be activated via auto-provisioning and is created for VoIP platforms that do not support Blind Transfer.

ParameterDescription
SipProvider.<0-9>.BlindTransfer

0 = Disabled

1 = Enabled (Default)

Example:

<?xml version="1.0" encoding="UTF-8"?>
<settings version="1.0" productID="e2">


<param name="SipProvider.0.BlindTransfer" value="0"/>

</settings>