Ans. -Voice over Internet Protocol (VoIP), is a technology that allows you to make voice calls using an active Internet connection instead of a regular Mob. SIM or phone line.
Ans. -DID (Direct Inward Dialing) is a virtual extension number of an ISDN or SIP trunk, also known as DID number or sometimes a Local Number of any particular destination.
Ans. -A toll-free phone number is one which you can dial without having to pay for the call. E.g. TFN start with 1800 in India and 800 in USA, respectively the series depends on any particular country.