Wolverine is part of Marvel, therefore Disney owns the publishing rights to the character. However, the film rights are still held by Fox, along with the rest of the X-men and The Fantastic Four.
As long as Fox owns the rights to Wolverine, they will not allow Disney to use him in the Avengers.
Right now, as i'm sure you know, a new Wolverine movie is in production set to release next summer. It was recently revealed that this Wolverine movie will take place after the events of the original X-men trilogy. It has also been stated that the next X-Men First Class film (2014) will deal with time travel and multiple dimensions. This will connect all X-Men movies. There are rumors of the Fantastic Four reboot (TBA directed by Josh Trank) will also tie in to the X-men films. This will give Fox a superhero franchise to compete with Disney's Avengers.
Also, Spiderman is owned by Sony, which means he will not partake in either X-Men or Avengers franchises.
As for Ant-man, he may be a lame superhero, but his movie is being directed by Edgar Wright, the guy who did "Shaun of the Dead', "Hot Fuzz", and "Scott Pilgrim Vs. The World", so it should still be a very entertaining movie.