Depends entirely on the vehicle but getting the voice buttons to work, assuming you get the 1.6.8 version of the PAC, is very tricky. They (PAC) don't have very good instructions, if indeed any at all, for most vehicles and the voice buttons. With my Nissan Titan, for example, the default instructions will get everything but the voice buttons to work, because the wiring for the latter is located in an entirely different spot.
The truth is, the PAC's are a generic device made to work with a wide variety of vehicles and a lot of the time it's a victory just getting them to control volume and track up/down. Right now I have mine doing that and mode switch; if I ever want my answer and hang up buttons to work I'll have to run a separate set of wires down under my passenger seat and use a meter to literally find which connections to tap in to since PAC support doesn't know either.
Also the PAC's (or any steering wheel adapter) cannot assign more than one function to a single button - this is more a limitation of the head unit than PAC. So for example if your voice control button also serves as, say, the button you push to pick up a call when one comes in, you have to pick one or another. The Pioneer itself is limited in the remote commands; it's not context sensitive for one, and I think with the x920bt it won't even accept remote commands for Voice Control, only answer call and hang up.
Bottom line, while you can expect to get the most common controls to work work you probably aren't going to be able to duplicate your current buttons exactly.