Random LAPDm MAC-block padding is not deployed yet
Recent versions of TS 44.006 (Version >= 6.7.0 from October 2008) specify that the BTS shall use randomized padding (fill bits) in its Layer2 frames.
This will help to combat the known passive A5/1 cracking attacks that rely on a small portion of known plaintext.
By using randomized padding, the amount of known plaintext can be reduced.
However, as of 07/2010, no network has been found to use this randomized padding.