If you only have an Ipad the most complete solution is Skype which is on Android (6.0+), iOS, Windows, Mac, Linux, Web, and Skype for Windows 10 and you do not even need an Ipad with LTE
Whatsapp if not used for a while does not need to be re-set up just your password or bar-code scanned
SMS is dying and the once unique offerings of Imessage are now a legacy, used mainly in one or 2 countries and I understand FBM still is more popular in US
The biggest elephant in the room with Ipad even with LTE is you cant be mobile and use an Apple watch
However we are digressing from OP original post