Questions

VOIP is an acronym for Voice Over Internet Protocol, or in more common terms phone service over the Internet.

Voice over Internet Protocol is a category of hardware and software that enables people to use the Internet as the transmission medium for telephone calls by sending voice data in packets using IP rather than by traditional circuit transmissions of the PSTN.

Here in the given options, Skype is the only voice service that enables us to talk over internet.

Channel of communication : It is a floe of communication within a department.

Skipper : This term is used for the status of a room, which indicates that a guest has left the hotel room without arranging to settle his or her account. 

Sundry Services :These are the extra services, which are provided to the guests. For e.g. message, handling of guests.

The one word substitute for "a person who is always dissatisfied" is malcontent.