Personally, I think that the sim module accessory would not be compatible with implanted comlinks because the implanted sim module is just that, the sim module (cold and hot sim possible). The simrig is just an upgrade on the normal sim module incorporating the devices necessary to access the simsense stuff without a trode net or datajack.
As to making a call with an implanted comlink, well, I think it's quite plausible since the implant could translate your thoughts into your "voice" for transmission and sent received signals to the appropriate sections of your brain to "hear" the other person talking. Now you probably would need an image link still to see the other person from a video feed (without going full VR), but so many people in the Sixth World blank out the video that that isn't a big deal not to have.
The Direct Neural Interface, that one I'm a little sketchy on, but due to that being the control of the VAST MAJORITY of cyber implants, the whole thing about a hacker hacking into your PAN and gaining control over your cyber is--to be quite honest--bullshit. Now the hacker might be able to mess with your smartlink and make it useless in that fight by making it target your allies until it's deactivated, but everything else is pretty much cut off from access other than your brain. (The wireless nodes in the cyber implants being there pretty much only for diagnostic and maintenance purposes with little or no REAL access into the systems)