I know many master's students who get an opportunity to talk to their potential PhD advisors well before applying. In most cases this opportunity is available by the professors with whom they worked for their master's. Moreover, there are many others who establish a contact with professors by mailing them and enquiring about PhD vacancies.

My questions are:

• How important is knowing an advisor prior to applying for PhD?
• Does an email interaction play a vital role when the department makes its admit decisions?
• If email contact is important, can a student send out mails to 2-3 professors (working in the same area) in case one of them does not bother to reply?
• To sum up, is applying of any use (especially in top universities) when you have no contacts and only your credentials to bank on?