Given the 'instantaneous' nature of intercoms I've largely given up on bothering.
It's still easiest to just SHOUT from across the house. That way you don't have to boot anything up, configure it, or maintain it's firmware.
I'd still like to find some cordless phones with intercom support. But most I've sampled just miss the mark in all kinds of little ways. There really is a gap in the market between office phones and residential expectations/requirements.