well i googled several years later wondering the same thing and it all comes back to this thread lol
i Googled "android remote sim mode" and it brought me to this thread.
SIM Access Profile (SAP, SIM, rSAP)
This allows devices such as car phones with built in GSM transceivers to connect to a SIM card in a phone with Bluetooth, thus the car phone itself doesn't require a separate SIM card. This profile is also known as rSAP (remote-SIM-Access-Profile).