The invention relates to a voice over internet protocol device capable of auto-selectively dialing up public switch telephone network or internet phone, said voice over internet protocol device can base on preset operation mode to detect if there is an in-coming call ringing signal transmitted from public switch telephone network thereon, if there is one, then the employment status of at least one terminal apparatus connected with said voice over internet protocol device can be based on making unused terminal apparatus be transferred to a loop which the said public switch telephone network is connected thereon.