According to this, Lydia Guzman of the group Respect Respeto is texting to a phone tree news about immigration sweeps that Sheriff Joe Arpaio is conducting in Maricopa County, Arizona. The texts are then broadcast to others in the tree:

Guzman said she sends the messages to a wide range of groups, including the American Civil Liberties Union of Arizona, Copwatch and various immigrant-rights groups such as Somos America and Puente. She concedes that some who receive the text messages likely use the information to avoid being caught and deported.

Per Arpaio: "This little group of people is (in favor of) open borders, and they don't like what I am doing. That is the bottom line... But it isn't interfering with our operations because every time we do it, we still arrest a good number of people, including illegal aliens."

Whether what she's doing is legal is open to debate; one ASU scholar says it might be illegal, and one from Vanderbilt says it's protected free speech. What would be interesting to find out is to what extent the ACLU is involved; who do they forward their texts to?

Note also that Respect-Respeto paid for current San Francisco police chief and then Mesa police chief George Gascon's trip to Washington DC to testify for comprehensive immigration reform.