The external call transfer – is the call transfer to a telephone line other than the company’s telephone line. The internal call transfer – the transfer of an incoming call to another addressee registered on the same telephone line.
Concerning practical implementation, the VoIP gateways have proven to be the best. Many companies are successfully using the IP telephony thanks to its two main characteristics
Decrease in international and long distance call cost expenditures
Stable communications between company’s offices throughout different cities and counties