Sequence locking/unlocking:
In the logs, dbus name :1.7 is mce (com.nokia.mce), :1.8 is the gconf part of mce, :1.46 is systemui (com.nokia.system_ui), 1.45 is the gconf part of systemui, 1.470 is the device lock keypad plugin of systemui
For the complete mce/systemui method calls look at the logs.

• same first 3 steps of pressing powerkey interaction
• selecting lock in the menu, systemui calls com.nokia.mce.request.powerkey_callback with value uint32=4 (I guess this is the menu value for locking)
• mce calls com.nokia.system_ui.request.powerkeymenu_close to close the menu, systemui will ack later with reply value uint32=0
• mce calls com.nokia.system_ui.request.devlock_open (uint32=3) to open the keypad, systemui will ack later with reply value uint32=1
• systemui calls com.nokia.mce.request.powerkey_callback with value uint32=-4
• mce calls com.nokia.system_ui.request.powerkeymenu_close again, systemui will ack later with reply value uint32=0
• systemui sends ack replies mentioned before, and updates gconf value /system/systemui/devlock/devicelock_autolock_enabled
• mce sends signal com.nokia.mce.signal.devicelock_mode_ind with value
  string "locked"
• mce updates gconf values /system/osso/dsm/locks/devicelock_failed and devicelock_total_failed
• after entering a code, systemui's device lock plugin will adquire a dbus name to send messages to mce
• now comes the interesting part, device lock plugins calls com.nokia.mce.request.validate_devicelock_code with two string values. The second one is a crypt seed for md5 (see man 3 crypt), the first one is the result of calling crypt with the typed code and the seed.
• mce receives the seed, so it can use it to call crypt with the unlock code stored in the device and check the result against the crypted typed code. If it is correct, mce will reply string "true", if it is incorrect, it will reply "false" to the previous call.
• systemui calls com.nokia.mce.request.devlock_callback with value uint32=3 if the typed code was wrong, and uint32=2 if it was correct
  If the typed code was wrong
• systemui calls com.nokia.mce.request.devlock_callback with value uint32=3
• mce calls com.nokia.system_ui.request.devlock_open (uint32=2)
• mce updates gconf values devicelock_failed, devicelock_autolock_enabled, devicelock_total_failed
• mce sends the locked signal again
• mce calls com.nokia.system_ui.request.devlock_open (uint32=3) again
  If the typed code was correct
• systemui calls com.nokia.mce.request.devlock_callback with value uint32=2
• mce calls com.nokia.system_ui.request.devlock_close
• mce sends signal com.nokia.mce.signal.devicelock_mode_ind with value
  string "unlocked"
• mce updates gconf values devicelock_failed, devicelock_autolock_enabled, devicelock_total_failed