Why can’t I receive messages from other phone not iPhone or ipad
Reciveing messages from a regular mobile phone not iphone
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By itself, an iPad is not capable of sending nor receiving SMS/MMS messages. Those are sent over a cellular telephone voice channel connection and require a cellular telephone. So an iPad is limited solely to internet based messaging services, like iMessage or Skype.
If you have an iPhone you can pair it with the iPad so the iPad can share the iPhone’s SMS/MMS capabilities. See - Use Continuity to connect your Mac, iPhone, iPad, iPod touch, and Apple Watch - Apple Support