In the UniFi controller after version 5.16, the SIP module can be disabled in the controller-

Disable the H.323 and SIP modules

But in the meantime, for the next couple of weeks the process that Ubiquiti recommends to disable SIP ALG is as follows:

SSH into USG 
the commands you need to run are:

configure 
set system conntrack timeout udp stream 30 
set system conntrack timeout udp other 30 
set system conntrack modules sip disable 
commit 
save 
exit

SIP ALG can be disabled by config.properties 
config.ugw.voip.sip_alg_disable=true

===================================/

August 2016

To disable SIP ALG (application level gateway) on this device:

Open the Command Line Interface

SSH into the router

ssh <username>@<ServerIP>

Run the following commands

* configure

* set system conntrack modules sip disable

* commit

* save

Exit

NOTE: The information provided above is from another OnSIP customer offering these settings for other customers with a similar device.  OnSIP does not sell nor monitor equipment and/or it's firmware updates/etc.  The settings of routers can change and are out of the control of OnSIP.  For best results, reach out to the manufacturer directly.

Optimize your network for business VoIP with the right router