VoIP - Support

When purchasing one of eXeTeL ADSL/HSPA service, is it compulsory to use your VoIP service?

No, you are free to use whoever VoIP provider that you prefer.

Why is my phone line provider billing me when I only make calls through the VoIP service?

It is very likely that your VoIP device has a backup system which automatically switches to the current voice service provider when the VoIP service is down.