But it gives us only the possibillity to instal 2,3 or 10 apps depending on the type of dev.account
Yes, it has to be dev. unlocked.
This trick only works on WP 8.1 and on phones who suports SD carts.
I use a free standart account so in this example i am limited to two apps.
But i want three apps, so how do i get that...........
Move the two sideloaded apps to your sd cart ( storage sense ).
Turn your phone off
Remove the sd cart.
Turn your Phone on ( without the sd ).
Now install the third app ( or a fourth ).
Then again, turn of your Phone.
Replace the sd cart and turn it back on.