There are some possible disadvantages to using VoIP services. These serves may not work properly if there is a power outage. If you need to call 911, the VoIP service may not connect seamlessly with the dispatcher. It may be difficult for them to trace the location of your telephone call if they would need to do so.
Another disadvantage of VoIP is that the quality of sound is not always the best. The person on the other end may have difficulty hearing what you are saying. Some VoIP services are also set up so that you can only call other people who use the same service and software.