I am pretty sure that the Pa-2A won't answer an incoming call and go off-hook. It has trunk port inputs, which means that it is not expecting ring voltage and can't answer an incoming call.

To be able to use the trunk port, you would need an FXO instead of an FXS. I am not sure that this would work either because the Shoretel may not seize the trunk line through SIP.

If the SPA112 could auto answer it MAY work if you set the PA-2A input to be a paging port, but I have a feeling that it wont.

I don't think this will work with the equipment you have in hand. There is a lot of other SIP paging adapters. Otherwise you may need to replace the PA-2A with a device designed to handle an incomine ringing call. Looking at the Viking website it looks like the FXI-1 may work. https://www.vikingelectronics.com/product-details.php?pid=568


I have never used this specific device, but it looks like it is designed to auto answer an incooming call.

David
Tele Express Business Systems