OK, I did some testing, and I found the following:
- Setup: two different users (Owner and user B with phone calls/SMS enabled)
- Contact database is not shared: user B does not see Owner's contacts, as reported by @de0u
- However, call history and SMS is shared: B does see Owner's history
This is quite a bummer. If you want to use this user B for maximum separation for a Googe/invasive profile, this profile will still be able to sniff and collect data on all phone calls and SMS you receive. Even if you only allow phone/SMS sharing on occasion (e.g., on first setup, or when receiving an activation SMS), the invasive profile will get access to all the history, unless you first wipe it from the Owner profile. This might have been obvious to some skilled users, but it was not obvious to me, although on a second thought it makes sense, as the phone/SMS subsystem is separated from the OS itself.
I still think this limitation should be emphasised more when discussing user profiles separation. For me, this is a no-go. At this point, the only alternative for me if I want to set up an invasive account is to never share SMS/phone with it, and rely on VOIP for emulation instead.