DACH - Deutschsprachige Community für Deutschland, Österreich, Schweiz

If you're taken into custody, as here. You get a notice to appear and a court date (about a week in the future). At the hearing you'd have an attorney assigned to you if you do not have one. Demanding lawyers of the facility staff won't do anything other than cause a conflict which you want to avoid for safety reasons.

You're almost entirely dependent on people outside of custody to get anything done. If you're going to be crossing a border you should have a friend of family member looped in who can track if you made it successfully or, if not, someone who can due all of the legwork for you, such as contacting an attorney, adding money to your facility account, etc.

You're effectively in federal prison while you're awaiting the hearing. Your movement will be limited to non-existent (you'll be in a cell solo, or in a dorm with 50-100 other people in a similar situation), you can't use a phone outside of approved numbers and you can send handwritten mail. If you're detained solo, you're likely going to be sitting in a cell until your hearing. If you're lucky, and have people's phone numbers memorized, you will be able to add someone's phone number to your list and you will get a free 15m call to each number that you added to your list.