Private calls in pre-trial detention are possible but require authorisation and are subject to the house rules of the detention facility.
Under section 188 StPO persons in pre-trial detention are entitled to contact with the outside world. Calls with relatives and other trusted persons are permitted but require authorisation by the facility director and are subject to any conditions set in the remand order. Frequency and duration are governed by the house rules of the particular facility. A remand order may restrict contact to specific persons.
What to do now: First, check the facility house rules for call times and the authorisation procedure. Second, file an application with the facility director for approval of specific phone numbers. Third, check whether the remand order contains conditions on outside contact and inform counsel of any restrictions.