How do I call or text an android user from my iPad?
You’re limited to internet only services if you don’t have an iPhone to pair it with. So an iPad by itself can make and receive VOIP calls (Skype, Ooma, other services with supported apps) or use internet messaging services (Google Hangouts, WhatsApp web, or any other of the plethora of internet messaging services with cross platform apps).
What you cannot do with an iPad by itself is make or receive cellular telephone calls, nor send or receive SMS or MMS texts as those too require a cellular telephone network voice connection.
This cannot be done. Your iPad is not a cellular telephone.
If, however, you have an iPhone, you may use Handoff to perform these functions on your iPad via your iPhone.
Use Continuity to connect your Mac, iPhone, iPad, iPod touch, and Apple Watch - Apple Support