@yablacky
I found my lock code using john the ripper as per the first 5 pages of ...
http://talk.maemo.org/showthread.php?t=37808

If I set the device to 'lock on SIM change' and 'Lock on first command'.
If I swap the SIM, I can just unlock with the code or send COM_UNLOCK from another phone. Then the new SIM will be added to the IMSI list?

I guess locking the device at all would be a bad idea.
A thief has three options on a dev_locked device:-
Enter the code correctly. (unlikely)
Lock screen and keys leave powered on. (would have to flick side lock)
Switch off the device. (most likely and prompted by UI)

Then if the device is switched off and secured SMSCON will not load!