You can stay 4 weeks without a phone? I don't think so..
I don't have a cell phone, Skype only and I don't miss it one bit. If you have to have a phone, how about doing odd jobs to earn money to pay for it yourself or live within your means? You know, self sufficient adult type stuff? If you are not lazy, you could probably earn enough in 2 weeks or you might impress the parents enough for them to chip in half. Win win.