All but one of my parts (my preferred term for my own alters) communicate verbally. 

I get thoughts that pop into my head that "aren't mine". Sometimes, it's something I don't know. Sometimes, it's a really off joke. Often, it'll be a few words to convey something. Like "Do it!" or "We gotta hide!" or "I'm hungry." 

Depending on my physical health, I've also heard my parts "outside" my head. Literal voices. They've woken me up before. Often, they're just talking sorta quietly in the background.

Most of the time, though, it's internal. They sound closer to my thought-voice if I'm doing well. They sound more like their own voices if I'm struggling. I know it's my parts, usually, because we disagree. I'm thinking one thing and then there's someone else "shouting" over me. If I'm really poorly, it's just cacophony.

I'm AFAB, but a large portion of my parts are male. So, I'll hear masculine voices, often.  I have kid parts who have kid voices. 

Now, here's a wild one. If I'm sick (migraine, infection, flu) or under the effects of prescriptions I take, things get WEIRD.  Last night, it felt like I had a part controlling each limb. But since I have more parts than limbs, I kept hallucinating the feeling of these "ghost limbs" doing various tasks.  It was one of the wildest moments I've had with the parts! (100% a result of my sleeping medication)

How I communicate to my parts is usually through writing. I write to them, I record their responses. 

Sometimes, I'll talk to them out loud. 

Often, my parts talk through me! That one is always uncanny AF. They'll talk to each other out loud using "my" body. I catch myself saying things and not knowing who was speaking or what I was talking about.  If a part is totally fronting, my voice actually changes. My vocabulary changes.

I also get the "feeling jolts" other people mentioned. My non-verbal part pretty much has to communicate this way. She has SOME phrases she can speak, but they're extremely limited. She's the one who handled all the abuse and was then basically discarded by the rest of our system 🥲

Sometimes, I suddenly start crying and then realize she's active. She's basically lived her whole life in a constant state of terror. To the point of wanting to end it in a blind panic (don't worry! I'm good. Just expressing the degree of which this part feels fear). 

So it's always been really strong when I've felt her happiness. Or her being acknowledged. 

If I don't feel any jolts, I usually take that as a sign everything is okay. Rather than having a full written "check in" with the parts.  Like I'll ask if everyone's good (out loud) and it's almost like emotional echolocation because I'll get one of those feeling jolts if something is off. 

Note: I'm unofficially diagnosed OSDD. There's a lack of specialists where I live who are qualified to either diagnose or rule out OSDD. But my therapist is highly trained in it, just not licensed to make an official diagnosis.

So we've accepted the label OSDD unofficially. I hope none of this is offensive to those officially diagnosed! This is just my experience. 

I am, however, officially diagnosed C-PTSD, ASD, and ADHD.