You do need hardware to convert the land line into digital so it can be used on your system, but a standard data modem will not do this.
You need a card for your system like a Digium, Rhino, Sangoma or an external device like an ATA to convert the analog line into digital so your system can use it.
I would still like to understand why a standard modem would not work?
Could it be that VoIP is digital and landline is possibly analog?
that still dont seem like a good explanation. If all I want to do is rout my own calls to a chosen number… Lets say all calls to my home mobile from my landline. whats to stop a script from converting the analog to digital?
I guess what the question is really… What is the hardware? and what does it do?
I standard modem is not designed to convert voice into a format compatible with VoIP.
There are many vendors that make hardware to convert Analog into digital. I listed 3 in my post above. This hardware converts the analog signal on your land line into digital so it can be used on a VoIP system.