When I go out with my bf or gf, they text each other. At first I didn't realize that was going on... He'd look distracted, flip open his phone, then shut it.. She generally would get a big smile before she put her phone away. Eventually someone texted something sooo good it had to be shared..
I find it cute that they keep in touch... Generally about twice in the evening... although it might be more often.
So the "no communication" problem isn't universal... Although they've been poly for almost two decades...