how about securing this phone ?

[Yealink Support]

Hi phlobot,

We have a solution for your request which can allow sip messages only from the registration sip server or outbound proxy server.
In the latest version, we just need to add a syntax using auto-provisioning cfg template.
Please add below syntax to your cfg.
---------------------------------------------------------------------------
#!version:1.0.0.1

#The x of the parameter "account.x.sip_trust_ctrl " ranges from 1 to max accounts. For example, x ranges from 1 to 5.

account.x.sip_trust_ctrl=1
------------------------------------------------------------------------------------------

When you want to enable this sip trust control for account 1, fill 1 to “account.1.sip_trust_ctrl”.
Then SIP messages from other servers will refuse by the phone.

Please kindly test and give a feed back to me.
Thanks for your cooperation.

@frankc
Please also try above steps to protect your phone.