Bob

The number they see will be the number they dialed.

You can set Google Voice/hang out app to be your default text sms app and then you should get the option to send text from which number, or at least that was the case on my last phone when I tried it as the default app.

Steerpike

To clarify, what I"m asking is - on MY phone - the receiving phone - when someone calls EITHER number, my phone rings and I see whatever Caller-ID they are giving out. But - I don't know which of MY two numbers they called.

1) My phone has two numbers - SIM Card number and GV number
2) caller with phone number 123-1234 calls me (on one of my two numbers). THEY know which number they called.
3) my phone rings. I see that caller 123-1234 is calling me.
4) my phone does NOT tell me whether they called my SIM Card number or my GV number.

Bob

I think the app says which number has been called to. It used to at least.

You can also set up different ring tones for each number.

I just have my default android phone caller as my phone app for the sim, and Google Voice app for the GV number though, rather than a one app dialer to control both numbers. Mostly because I didn't like the dialer and especially the sms aspect of the Google app and have just stuck with keeping it this way.

Steerpike

I think that's the way I need to go. By default, when I installed GV, the number became 'tightly integrated' with the stock android dialer / receiver. The GOOD thing about this is - when I try to make a call out, it forces me to choose so I can't accidentally call out with the wrong number (such as, if I want to call my customer and don't want to reveal my personal #). So that's a plus for the integration with stock dialer side. But (both types of) incoming call just 'rings' the stock 'answer' piece. If I uncouple them, I PRESUME when someone calls my GV Number, the Google Voice app alerts me, rather than the stock android 'answerer'. Then if I call them back, I just need to remember to launch the GV app and not the stock app.
Complicating this is the fact I'm making good use these days of google assistant (For hands-free calling). Currently, I can say 'ok google, call john smith' and it 'works'. I think, however, I can say, 'ok google, call john smith using google voice' . Not sure what I'd say for the stock app thought - maybe just 'ok google, call john smith'?

I guess I will just have to try it! I'm not sure how to decouple them but I'll figure it out.

Bob

If you don't have Google Voice integrated as default dialer, I think if you ask Google to call someone, it asks you which you want to use to make the call.