You wouldnt use it everyday.
At my school there are like 15x phones, each of the 4 vice princpals have one who let u use them, there is one at student services one at administration one in each of the 6 house leaders office and then 4 public ones around the school. The vice principal lets me into his office 24/7 to study and not go to class lol, and 90% of the time he leaves for long periods at a time. Also at student services there are like 5 different people who work there hence use it on different days when different receptionists are there.
You could regulate 3 a week easily without causing suspicioun. Probally even up to 5
I would go
Monday - Student Servies
Whenever i was in VP office
Thursday - Student Services
Anyways sorry to wreck your topic lol,
if u want more info/other ways just pm me..