Crikey! Many ways of skinning this cat!
I use the NAV as the core which controls everything. I have an SD card in there with hundreds of MP3 tracks. I like the NAV to control everything as it's right in my line of sight. Also it "prioritises" everything, so if you're on music, and a call comes in, it will give priority to the phone call for instance. It will also speak the directions to you from the NAV as a priority (i.e. turn left in 200 metres), cutting or quietening the music whilst it speaks the commands to you.
My phone is bluetooth with the NAV (no phone to intercom connectivity for me)
So I can play music off the NAV, and the NAV also controls incoming (or outgoing) calls. The phone book is replicated on the NAV, and an incoming call pops up on the NAV with the usual green (answer) and red (decline) buttons.
If you don't want to talk to anyone via intercom (passenger, or another biker) then almost any bluetooth headset will do. Something like a Interphone Connect probably (I only say this as I have one and it's worked well with great battery life)
https://www.sportsbikeshop.co.uk/motorcycle_parts/content_prod/450915 (you could spend a lot less, almost any unit will do)
I have never tried phone to intercom direct connection, as I like to see who is calling etc and control the call from my nav screen (I keep my phone tucked away, not in view)
If you only want to talk to one other person (pillion), then bluetooth comms is OK. If you want to talk to other bikes or a group, then you'll need to be aware what units they have, as the two market leaders (cardo and Sena) don't really talk to each other easily. MESH2 has redefined bike to bike comms as it's an open protocol but only currently on higher end units from Interphone (UCOM 16) and Sena (30 and 50 range IIRC). MESH2 works great in a group or riders and is a one-button-click to set up, and the range is excellent.
Moving off topic a bit, but some NAV providers seem to be developing VHF for inter-bike comms. That could indeed be a game changer! (Garmin Tread for instance)