[2015-06-30] unlock jolla phone, from permanently locked mode

Put your phone into the Recovery Mode:

  1. Power off your phone, disconnect from all cables
  2. Remove the battery
  3. Hold down the Volume-Down-Button
  4. Insert the battery again
  5. Push the Power-Button
  6. Release all buttons as soon the phone vibrates
  7. Connect your phone with the PC via USB

Now you should have a second network interface, and now you can use telnet to access the recovery menu.

telnet 10.42.66.66

Just select number 4 and enter your device lock code.

----------------------------
     Jolla Recovery v0.3.1      
----------------------------
Welcome to the recovery tool!
The available options are:
1) Reset device to factory state
2) Reboot device
3) Bootloader unlock [Current state: locked]
4) Shell
5) Try btrfs recovery if your device is in bootloop
6) Exit
Type the number of the desired action and press [Enter]: 
4

If you continue, this may void your warranty. Are you really SURE? [y/N] y
Type your devicelock code and press [ENTER] key:
(please note that the typed numbers won't be shown for security reasons)
[OK] Code accepted.

modify the devicelock settings file

mount /dev/mmcblk0p28 /mnt
sed -i "/nemo\\\devicelock\\\maximum_attempts=/c\nemo\\\devicelock\\\maximum_attempts=-1" /mnt/usr/share/lipstick/devicelock/devicelock_settings.conf

disconnect the phone and reboot it.

I found the info on this zendesk page