Do not leave me a voice mail that simply says “please call me” and nothing else. Give a reason why you need to take up my precious time (preferably a billable one) or I won’t call you back. If the reason isn’t important enough to bother mentioning, then it’s not important enough for me to bother returning your call. If the reason is too complex for a voice mail, then send me an e-mail. This applies doubly to people who work at the same firm.