Table schema:
CREATE TABLE Students (cell_mobile_number VARCHAR, student_id VARCHAR); CREATE TABLE Student_Addresses (student_id VARCHAR, monthly_rental VARCHAR)

Question: What is the cell phone number of the student whose address has the lowest monthly rental?
SQL: SELECT T2.cell_mobile_number FROM Student_Addresses AS T1 JOIN Students AS T2 ON T1.student_id = T2.student_id ORDER BY T1.monthly_rental LIMIT 1