Setup extensions to always be in call

I have 2 sip adapters that i need to setup to be always in call, meaning i have a voice path between both devices all the time. the device will not have a standard telephone connected to them.

Is there a way to setup asterisk to have these 2 devices all ways in call without have to use a phone to dial the other side?

Ideally, this should be done by the devices. In fact, if they are permanently connected, they should probably not use the services of a PABX at all.

However, some combination of startup scripts, Originate, call files and h extensions should be able to establish the call on startup and re-instate it if it drops out.