How do I install Sangoma Talk on devices that do not have access to the internet?

Commercial Modules Sangoma Talk / Software Phone
1

Hi,
I am wanting to test Sangoma Talk (ST).

My FPBX deployment is on a pc connected to my local work network. The FPBX server is behind a company firewall. The company firewall does not currently have any FPBX ports open. Local Yealink phones register and work as expected.

I have three types of devices.
Type 1.
iOS (iPhone).
These devices are allowed to make outside calls and dial internal extensions.
They have an unlimited data plan and is always connected to the internet via cellular.
The phone needs to connect to the FPBX through the company firewall from external.
The ST app fails to register. This is not my question because I know the company firewall ports are not open.

Type 2.
iOS or Android phone with limited data plan.
These devices are allowed to make outside calls and dial internal extensions.
When not at work, connected to cell provider and will connect to FPBX through the company firewall.
When at work, connected to local work network via wifi and should connect directly to the local FPBX.
Phone has limited access to the internet through the firewall.
When at home, connected to home wifi and will connect to FPBX through the company firewall.

Type 3.
iOS (iPad)
These devices can dial internal extension but are not allowed to make outside calls.
Always connected to work wifi. It should connect directly to the local FPBX The iPad is not allowed access to the internet.

Type-2 and Type-3 devices.
The ST app fails to register. I believe this is because the app expects to have access to the internet. My company firewall prevents this traffic.
I would think that since the FPBX server is local, the device should only need ext/secret credentials to register.

Type 2 question.
When I arrive at work, my phone connects to work wifi. I want the ST app to re-register with FPBX to use local network.
When I depart work, my phone drops wifi and reverts to cellular data. I want the ST app to re-register externally.
How do I setup ST so that automatically re-registers based upon connected locally to wifi or connected externally to cellular data?

Type 3 question.
How do I setup ST on a device that is not allowed access to the internet?

Thank you,

2

I’m an Android person, and haven’t used Sangoma Talk, but I assume that the same rules apply to telephony applications on iPad as on iPhone and that they will be put to sleep in a way that requires a push service to wake them up before they will listen for an incoming call. I’d therefore assume that they need access to the push server used to support Sangoma Talk, which will be on the public internet.