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If you want to switch over to VoIP instead of PSTN all you need to do is choose a VoIP service provider. Most of these providers are situated in the United States. Some VoIP service providers are: Vonage, BroadVoice, iConnectHere and Lingo.
For a monthly fee of $8-$20 they will provide you with features such as voicemail, [...]

In order to make calls with VoIP, you will need a telephone which can be connected to the World Wide Web. If you wish to use a standard phone with VoIP you can get an Analog Telephone Adapter. This will digitize your voice and enable you to make phonecalls with VoIP. This adapter has an [...]