Yes, it does affect your internet speed. While you're using the Voip service, the transmissions between you and your destination are continually using the internet bandwidth that you have. However, on most internet services this is a very marginal, or insignificant amount. If you were on a low speed DSL or wireless service however it may not work, it may reduce voice quality, or it will significantly reduce the effectiveness of your internet usage while you're using the VoIP service.
