I know that Square, for instance, makes payment card readers you can attach to phones in order to make transactions using the mag strip, and they're soon to release a new card reader designed for EMV chip cards, but are these necessary for Android phones?
My understanding is that tap-and-pay using Google Wallet or Apple Pay (or the like) use the same technology and technique to authorize a transaction as EMV chips do. If that's the case, is it plausible that one could create a program that allows the phone to act as the point of sale terminal instead of as the client? If not, please help me understand how these technologies and/or communication methods differ. Thanks!
Edit: I just found out that some EMV chips support NFC while others need direct contact, and that most American cards don't support NFC, including mine.