A lawyer should always be willing to answer any questions you may have regarding your case.
However, the most common complaint made about lawyers is poor communication. It's a shame, because in my experience clients can often be very helpful in developing an effective defense. Often times critical facts not apparent in the police report can only be provided by the client.
Of course, one can't expect one's lawyer to always be available to answer every call. But messages should always be returned in a timely manner - preferably the same day. And if the matter is particularly urgent, that includes weekends.
I make it a point that my clients have my direct line, and much to my surprise, very few clients abuse the privilege.