The PvP battleground call to arms is being removed in Warlord of Draenor. This is being done in due to the negative influence the call to arms had on queues.
Quote from: Blizzard
We’ve removed Call to Arms in Warlords. Originally, the feature was added to bring some variety to the battleground experience and allow players who like a specific battleground to occassionally binge on it. But, like any feature, we have to weight the benefits with the consequences. Call to Arms has an adverse affect on queue times in a pretty profound way. When certain battlegrounds are up, one faction will tend to queue for Call to Arms while the other tends to avoid it. As a result, we’re going to remove it so that the majority of players are queuing through Random Battlegrounds.