Waiting for a call is not your only option. You can get information directly from the facility if you approach it the right way.
Call the facility and ask to speak with your inmate's counselor. That is the person most likely to have specific information about the SHU placement, including why it happened, what the disciplinary finding was, and how long the placement is expected to last. Counselors manage the caseloads for their assigned housing units and have access to disciplinary records and projected release dates from segregation.
The approach matters significantly when making this call. Staff are more responsive to people who are calm, polite, and respectful than to callers who come across as demanding or confrontational. Lead with who you are and your relationship to the inmate, keep the request simple and direct, and thank whoever helps you regardless of how much information they share. A humble tone goes a long way in these conversations.
Not every counselor will share specific details about a disciplinary placement over the phone, particularly if you are not listed as an emergency contact or official family member in the inmate's file. If the counselor is unable to help directly, ask whether there is someone else at the facility, such as a unit manager or the disciplinary hearing officer, who can provide a general timeline.
In the meantime, sending a letter through InmateAid is worth doing regardless of what you find out on the phone. Mail reaches inmates in the SHU and having something from you arrive during that stretch means more than it does during normal population time.