I don't use voice mail and would love a phone-based application that will record messages. Callers wouldn't even know what system you're using when they're asked to leave a message, so if they'll leave a message on voice mail, they'll leave one on a phone application.
So why don't I use voice mail? Because I have to pay to access it and most times it's a waste of time as I know that someone has been trying to contact me anyway and if it's someone who matters I can call them back.
We don't all live in the U.S. you know! I go to mainland Europe frequently and if I had to be continually accessing voice mail for messages left by U.K. callers, it would cost me a lot of money.
I'm sorry to say this but occasionally I find the attitude of some members of this site very irritating. When a member asks for an app such as this, I assume that there's a good reason why he wants it. Others just seem to suggest that he's some kind of idiot because all he has to do is turn on his voice mail! Give people credit for knowing what they want and don't assume that everyone lives in the US, never goes to a foreign country and gets free voice mail access. Some of us don't fit the stereotype!