a few basic questions about NFC, NDEF and NFC enabled android phones

Question

I want to start android programming to be able to transfer data between a NFC enabled smartphone and a custom device, but I am not able to find clear information about a few things

For example, my custom device has to be able to send data to the smartphone as well as receive from it. But from what I have read it is not currently possible for two way communication using NFC
How to send data between two devices using NFC in android?
or the more recent,
NFC enabled phone act as a NFC tag
But the Android developers website itself says that we can use Beam to perform peer to peer communication between two android phones, so two way communication should be possible shouldn't it?

Android Beam allows simple peer-to-peer data exchange between two Android-powered devices. The application that wants to beam data to another device must be in the foreground and the device receiving the data must not be locked. When the beaming device comes in close enough contact with a receiving device, the beaming device displays the "Touch to Beam" UI. The user can then choose whether or not to beam the message to the receiving device.

http://developer.android.com/guide/topics/connectivity/nfc/nfc.html#p2p

Secondly, can I use an android NFC phone as a tag writer (instead of just a reader)? That is, just send data to my custom device (or a passive NFC tag)?

Answer 1

The keyword in "simple peer-to-peer data exchange" is simple. Currently (Android 4.2), apps cannot do 2-way communication over Beam. However, a custom device can send multiple messages over Beam. All of these will be received by the Android device without problems, but the Android app can only send one message. You can trick the Android device, however, by resetting the RF field in your custom device. It will appear to the Android device as if a new device has appeared and it will show the "Touch to Beam" UI again.

Android NFC devices can act as both tag reader and writer.