How easy is it to link a cell phone to a crime to get a search warrant for it?

This is something I’ve been seeing more and more of: A co-conspirator’s cell phone is seized and another co-conspirator’s number is known to be on the phone. A search warrant issues for the other cell phone for its contacts, text messages, call logs, and voicemails. These days, probable cause for the crime + known use of a cell phone = probable cause to search the cell phone.

Thus, a co-conspirator in a home invasion robbery had another’s cell phone number in his phone. With probable cause to believe defendant was involved in the robbery, there was probable cause for a search warrant for his cell phone, too. United States v. Harris, 2016 U.S. Dist. LEXIS 169232 (E.D.Tex. Nov. 4, 2016), adopted, 2016 U.S. Dist. LEXIS 168804 (E.D. Tex. Dec. 6, 2016):

Here, there is sufficient information in the affidavit linking Defendant Harris and his cellular telephone to the armed home invasion robbery on December 9, 2015. During the investigation, a co-conspirator identified “Jermaine” as a participant in the armed home invasion robbery on December 9, 2015, and provided telephone numbers of “Jermaine” and other co-conspirators. According to his affidavit, Agent DeLoach observed a “contact card” on the co-conspirator’s phone with the name “Jay Jermain (Big Bro)” and telephone number (xxx) xxx-7904. After obtaining telephone records for the number associated with “Jermaine,” law enforcement determined that Defendant Harris was the subscriber of said telephone number. Defendant Harris was further identified by a co-conspirator through a photograph. Defendant’s argument that the Government failed to establish the reliability of the co-conspirator is unpersuasive, given that the information provided by the co-conspirator was corroborated by other electronic and physical evidence.

Moreover, even if probable cause had been insufficient here—which the Court finds that it was not—the Court finds that law enforcement acted in good faith reliance on the search warrant when executing it. …