According to TV@Spreadit.org:
Entourage season 7 episode 10 called “Lose Yourself” which was directed by David Nutter and written by Doug Ellin did not air this evening on HBO but will be broadcast on September 12, 2010.
As you eagerly wait for Entourage’s heated finale which will explain how the friends end up losing all they have worked for – here is the preview of the upcoming installment:
Mrs. Ari is still fuming over Ari’s angry meltdown the night before, Ari tries desperately to keep her surprise party on track. The guys attempt to stage an intervention for Vince, who has gone off the deep end. Turtle scrambles to find investors to save the tequila business. Eric receives an unexpected request from Terrance McQuewick, which leads him to consider Scott’s business proposal. Robert Pattinson guest stars as Ari’s most difficult client ever.
And From eWorldPost.com:
There are more reasons for a person to tune into HBO on the 12th September. Apart for the usual crew of the show that has amused the people over a long time, a surprise is expected. It is surprising but true that in this episode, the star of the Twilight Saga, Robert Pattinson will make a guest appearance.
Most of the sites like HBO, TV.COM, TV Guide or IMDB still don't say anything about him being a guest star on the show, but we never know. Christina Aguilera is on HBO's preview of the episode, and she isn't listed in any of these sites either.
A couple months ago, Mark Wahlberg talked about a possible Rob cameo and his comment was "Yeah. We'll see about that."