The first thing I can think of about VOIP is that 911 (ie, emergency calls) are not available with these services.
For me, this is totally unacceptable.
Skype, for instance, says in their agreement that emergency calls are not available.
Based on that alone I would say they shouldn't be used as a replacement for a land-line that provides this service.
Unless, of course, you feel that you don't need it.
VOIP services are less expensive; that's the plus side.
They also don't offer the stability; that's the negative side.
If the 'grid' goes down for any reason, then the internet goes down, too (that includes VOIP [Voice Over Internet Protocol]).
Whereas, phones don't depend on the grid- they are on a separate system.
If you don't believe me, then think about how many times you've lost power, but the phone still works.
(This presumes you have something other than a wireless phone system in your home.)
Your call... no pun intended
Just a thought.