AAH and Soft Phones

I have an option. I could sign up for like a $6/month VoIP service, install AAH, and have everything run over IP and use soft phones with no problem.

However, my second option is this: I have one of those $10 WildCards off of eBay, and I can use it with Asterisk and with my current phone service provider, which is not VoIP. My question is this: Can I use ethernet softphones on the computer with this setup? If so, how does it work? Do I have the phoneline plugging into the computer along with a network cord into the LAN?