No, there is no need to dial a special number. Making and receiving calls with the VoIPtalk service is the same as with a standard telephone/mobile. For calls within the UK you have to dial the full number including the area code and for international calls dial 00 followed by the country code.
To dial other VoIPtalk users, simply dial their VoIPtalk ID from your VoIP Phone. All calls to other VoIPtalk users are absolutely free.