In order to provide seamless VoIP service in the mobile wireless environment, we need to minimize the disruption time to process a handoff of an ongoing VoIP call. There are several schemes focusing on this issue. However, they require a lot of signaling message exchanges, resulting in exposures of confidential information of the mobile nodes in network. We propose a Dynamic Shadow Registration scheme eliminating these disadvantages. Our simulation results show our scheme can significantly reduce the message overhead with maintaining almost the same handoff delay with other schemes.