As the topic starter I can tell you that the SPA942 are from an old company I worked for in 2010. I found them in my garage and wanted to try and see if I could set up an internal phone system since my wife have her office upstairs and I have mine downstairs.
We have our fibre from orange in Spain and they do not route sip traffic beside their own on fibre to private customers. But we have a sip account in our firebox that only can be used with a PSTN equipment.
So what I tried was to set up freePBX with the 6 SPA942 I have and then configure a SPA3102 (that also was in the box with the phones) to be able to have a phone system in the house and use the free phone service we have included in the fibre connection.
But everything is solved and we have 6 extensions that can use our sip->pstn->sip gateway to both make and receive calls.
All for free and I have learned a lot during the setup.