The following are the components of a corporate Internet telephony solution for international calls:

1. Access Devices
Software or hardware interface used for initiating connection and making call. Example: IP Phones, Analog Phones with VoIP Gateway, Soft Diallers installed on PC's with Headset, USB Digital Phones etc.

2. Network
Either Internet with data and voice on same network OR Dedicated voice bandwidth. The customer has two options either he uses his existing Internet network to transmit both data and voice on the same network or he chooses to take a separate channel for only voice transmission.
If he chooses the first option and uses his existing Internet connection for making a voice call, it may lead to problems in voice quality. This happens due to congestion in the network.
Congestion arises because both voice and data packets compete for the same bandwidth as the customers is using the same network for surfing, data transfers, mailing and now for voice as well.
Congestion negatively impacts voice because Voice is a Real Time Application, which means that the data that carries voice has to reach the receiver in real time for it to be useful. In case there is a delay in the voice data reaching the sender, the quality suffers.
Commonly faced problems are:

a) Voice breaking during the call
b) Call not getting through.
c) Echo
d) Jitter (voice fluctuating)
e) Warbling.

For best voice quality the customer should use a clean pipe for carrying voice from the access device to the internet telephony server and from there hope to get the cleanest pipes to the PSTN cloud.

That brings us to the second option wherein you use a clean channel for voice with no data on that channel from the customer office to the Internet telephony server in the US. One voice channel requires 17 - 24 kbps. So 4 channels of voice would require approx 96 KBPS i.e. about 100 KBPS.

3. Internet Telephony Services(VoIP Minutes)
VoIP Minutes are required to initiate calls from Access devices onto a PSTN or Mobile network in countries abroad. These VoIP Minutes are available in different forms as calling cards with account ID and Pin very similar to a mobile recharge voucher.