Last week the patch notes for 6.2.4 were released, simply stating Battlenet optimizations.

However, on the UI forums, a more detailed post mentioned that support for Battlenet conversations was being removed. Battlenet whispers are still enabled. Players on the PTR have confirmed that they are unable to make conversations with friends and that the code is missing. There is no word yet from Blizzard on why they are removing this feature or whether something will be added to replace it.

Y'all deserve a heads-up before this thing goes live, as it's a bit of news that isn't being spread very well by Blizzard. After 6.2.4 hits, we will be going back to older methods for cross-faction RP in groups, though at least we will still have individual whispers. I might be AAMS, but I'm not really looking forward to that.

Relevant threads:

Patch Notes:
http://us.battle.net/wow/en/blog/19996972

US UI/Macro thread:
http://us.battle.net/wow/en/forum/topic/20742784697?page=1

EU Thread (with lots of RPers chiming in)
http://eu.battle.net/wow/en/forum/topic/17610751003?page=1

US General Discussion Thread:
http://us.battle.net/wow/en/forum/topic/20742604806?page=1