Q: Can my iPad answer incoming calls thru handoff&my iPad's cellular data line,without WiFi internet? If that is possible,will it still work if iPad&IPhone have different cellular companies(AT&T&Verizon)?

...Can my iPad-mini (original) answer incoming calls through handoff and my iPad's cellular data line, without a WiFi internet connection?  If that is possible, will I still be able to answer incoming calls on my iPad, if I have my iPad on one cellular service (AT&T, with a cellular data line), and my IPhone6Splus on another cellular service (Verizon)?  Or do I need to keep both iPad and iPhone running with the same cellular service company? 

...Both iPad-mini & iPhone6S will be kept upgraded to latest iOS, and both have maximum RAM = approximately 128GB.