The term "Osaifu-Keitai" itself is a registered trademark of NTT Docomo.
FeliCa, developed by Sony, is the standard technology used for Japanese smart cards.
Osaifu-Keitai can provide more convenient services than plastic FeliCa cards.
For instance, it can automatically recharge itself via the Internet, or provide the latest information.
Osaifu-Keitai basically functions even without radio transmissions, so the applications can not be terminated just by closing a phone account.