Can a phone emulate an NDEF tag for another phone?
On Android, yes. A host card emulation service that registers the NDEF Tag Application identifier and answers its commands presents the phone as a Type 4 tag, which any reader reads. The other phone has to be reading rather than emulating, and peer to peer mode is gone from both platforms.
A Type 4 tag is a set of answers
Nothing in the Type 4 sequence requires a chip. A reader selects the NDEF Tag Application by its identifier, selects the capability container file, reads it, then selects and reads the NDEF file, as the Type 4 page sets out. Code that answers those commands with bytes of its own is, from the reader's side, a Type 4 tag.
On Android that code is a host card emulation service: it registers the identifier in its XML, as the implementation page describes, and answers the SELECT and READ BINARY commands that follow. The constraints of the mechanism apply unchanged: ISO-DEP over NFC-A, one logical channel, an exchange kept near the guide's thousand bytes so the tap stays short.
It stays an emulation. The reader sees a message, not a tag identifier that a chip would carry, and the content is whatever the service decides to answer at that moment, which is the point of doing it this way.
Both sides cannot poll at once
A phone that emulates is answering a field, not producing one. So the other phone has to be the reader, and to be reading deliberately: reader mode suspends card emulation for as long as the activity is in the foreground, which the reader mode page sets out beside the alternative.
The emulating phone brings its own conditions. Whether it answers with the screen off or from the lock screen depends on the Android version and on a device setting, which the screen off page takes version by version. A demonstration that works with both screens on can fail in a pocket.
What an iPhone does here
An iPhone reads this without anything special. Core NFC reads NFC Forum types 1 to 5, so an NDEF session asks the emulated tag the same questions it would ask a sticker, and the answers decide whether it works.
An iPhone emulating is the constrained direction. It takes a card session, from iOS 17.4, whose entitlement Apple grants on application and whose identifier list would have to include the NDEF application; the iOS emulation page covers what that involves.
What peer to peer left behind
The mode built for two powered devices is withdrawn from both mobile platforms, as the peer to peer page recounts. What remains for two phones is this arrangement: one emulates a card, the other reads it.
That is enough to hand over a short message, an identifier or a link, and it is the wrong tool for a file. NFC earns its place when one side has no power and no screen; between two phones with both, a radio that reaches further carries more.
Frequently asked questions
Does the reading phone need a particular app?
Yes. Something has to read, through reader mode or an NDEF read, since the emulating phone is answering rather than polling.
Can both phones emulate at the same time?
No. An emulated card answers a reader, and two cards never meet. One side polls, the other answers.
Can an iPhone emulate an NDEF tag?
Only through the gated card session, from iOS 17.4, where Apple grants the entitlement. Reading one takes nothing special.
Is Android Beam still available?
No. Peer to peer mode has been withdrawn from both mobile platforms, which is why emulation is what remains.