At work we use RFID cards to get through the doors. I don't like to carry it hanging from the neck. I wanted to put the rfid card in my phone, which is the only artifact (beside my wristwatch) that I carry with me all the time.
One problem: the card is too thick to fit inside the phone. But it's mostly made of plastic, so my idea was to somehow extract the chip and antenna from the card.
If you have a Siedle RFID card, which looks like the picture, and want do do the same keep reading: