The United States Constitution (and those of most states) contain a clause that prevents the government from denying folks "due process of law." In the DMV context, due process means that the state cannot suspend your driver's license permanently without first giving you the opportunity to contest it at a hearing. Lawyers call this the "right to be heard."
If you've been given a notice that your driver's license will be suspended, you'll be given a pink notice of suspension with some fine print. It advises you that your license will be suspended in 30 days if you do not request a hearing within 10 days. You can either call or write DMV to request a hearing, but either way, you should demand an in-person hearing and object to testimony by telephone.
These simple techniques will help you maximize your chances of winning your hearing because they make it more difficult for DMV to establish the proof it needs to suspend your license. For example, where DMV needs a witness to appear to testify against you, they often to not actually appear if you make them show up in person.