At the end of the midseason finale, Tara picks up her phone and does something. Far away, Deathstroke picks up his phone and sees that someone sent him a message, "I'm in." So after seeing this, many people would just link the two together and think that Tara texted Deathstroke. But I don't think Tara was contacting Deathstroke. (You can come yell at me if the truth is revealed and I'm proved wrong in June.) I don't believe that the producers would just go along with the Judas Contract storyline that we've already seen so many times. They will probably make a thrilling twist to the story and astonish us all.
First of all, Tara was only seen using her phone. They never even showed what she was actually doing. It isn't confirmed that she was texting Deathstroke, or even if she was texting someone. Yeah she looked behind her shoulder to check no one was looking and sure that looked suspicious, but maybe she just wanted some privacy so she could read the news (like Brion did), or something like that.
Second, Deathstroke received that text from an anonymous person. The sender was never identified. It could be anyone. The scenes were probably just put close together to create suspicion.
Lastly, the producers are known to not follow mainstream comics. Artemis is a villain in the comics, but here she's a hero; Halo is very blonde, white, and a little silly in the comics, but here she's a dark-haired Quraci; and this version of Kaldur is vastly different from the comics; etc.
So what really happened in this scene?