Mobile Data only phone?

Privacy and Security Get Advice
1

I got a graphen os phone pixel 6a
until now i am using it as a wifi only phone
i got no phone number, because there is no reason to have one for me
if i had one, i would never call over “normal” phone, because it’s not secure
there are better options, like signal calls or calls over other secure messengers

So is it a good option to just choose mobile data, without calling?

2

I only make voip calls over signal, that’s practically my only option. I never connect to wi-fi, not even at my house.
My concern with using my normal phone number has been contact tracing. Slowly I’m moving my contacts to a 90 day mint mobile plan. Frustrating for them that they have to change my number every 90 days.
I guess for my threat model I can use my normal phone for calls because in 90 days that number will be useless to contact me. The people i contact over the phone or more of a privacy issue vs security as of now.