He either:
a) snuck in a phone, or purchased a "pay as you go" phone during a walk or scheduled activity outside of the center, and is likely going to get kicked out, because patients ALWAYS get caught and/or rat on eachother for this type of behavior.
b) got kicked out or left voluntarily.
No inpatient rehab allows cell phones. (Unless he's in some type of "extended care" program, which is a different story.)
Experience: 3 inpatient rehabs myself.