Not  necessarily. If you have a mobile phone, they can use "wifi calling" and Apps like WhatsApp has the ability to do face to face or voice calls.

The named Software Apps can have limitations though. 

Facetime (Apple) only does Apple to Apple calls.

WhatsApp (all systems) only does Mobile to Mobile Calls. 

Zoom and Teams (all systems) requires you to have their respective Apps. 

Specific VOIP apps (known as softVOIP ) allows you to call Mobiles, or handsets such as YEALINK or old analogue phones using an ATA device. 

VOIP Handsets in turn can call mobiles, or soft VOIP apps.

So getting a VOIP connetion gives you the widest ability of contacting people.