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In this paper, we study the voice portal services in packet network and VoIP environment. An extensible VoIPTeleserver for VoIP in SIP (Session Initiation Protocol) environment is described. It is based on the concept of dialogue system and web convergence that separates the channel dependent media resources from the application creation environment. It supports XML based service applications for multiple channels including voice, DTMF, IM and chat over IP. Special attention is given to the adverse effect of delay, jitter and packet loss for voice portal services over IP. In particular, case studies of DTMF service in voice portal under adverse channel conditions are performed. The compounding effects of multiple channel impairments to DTMF in voice portal services over IP are revealed. The potential high error rate indicates that the data redundancy method as proposed in RFC 2198 is needed for DTMF in order to achieve reliable voice portal services over IP.