just a few ideas but

how hard would it be to have a 2nd number/email address registered in the phone where if you change sim cards it automatically sends a sms/email to the registered account asking for permission to use that sim (with phone number)

you send a txt back saying yes or no and it comes up onscreen saying please enter password and starts encrypting everything in the background after the 2nd try no matter whats entered it will say password accepted and appear to work but wont make outgoing calls send txt messages or open any programs and then after 5mins timeout and the screen and keyboard powers down appearing as if its turned off

gps turns on and saves a log of GPS co-ordinates where the phone is in the same area for more than 10 minutes

it also autodetects any free wifi networks and emails/txts the log to your email/phone

if you end up getting your phone back you can simply unlock and unencrypt the device by putting in your 2nd sim and entering a password or connecting it to a registered computer