In other words, Google Voice requires you to have a separate telephone number, that's not your mobile phone number. Depending on what services they want, people have to contact you on the two separate numbers. (Google Voice has limitation on SMS, international calling etc.)
No, Google Voice requires you to have a Google Voice number [full stop]. It doesn't matter whether you have a mobile phone number or not. Even if you do have a mobile phone number, nobody ever has to know it or call it, because they can reach your cellphone anyway (either by you setting up Google Voice to transparently forward to your mobile phone number, or by using a [VoIP] data connection with Hangouts). If you continue telling people to call your "real" cellphone number after signing up for Google Voice, you are proverbially Doing it Wrong.
You could cancel your cellular service entirely and use your phone with Google Voice over wi-fi, or get a plan where you only care about the data part and the "voice" minutes are irrelevant. For example, my T-Mobile plan costs $30 and has 5GB of 4G data (which is equivalent to about 4000 minutes of VoIP) and a measly 100 actual-voice minutes. But that's okay, because I use exactly 0 voice minutes because all my calls are routed over Google Voice. Since I don't come anywhere close to using all 5GB each month, I could probably even switch to a provider like Ting, select a data-only plan, and pay even less.
And by the way, Google Voice does in fact have SMS and international calling (the latter has some non-zero per-minute cost, though). I don't know how you imagined it didn't.