SSG: How old are you? You have the income to support a family and medical bills and stuff? If not, my suggestion is to get a new cell phone. Maybe skip town for a bit.
Sounds shitty, but if you're not ready to be a dad, them's the breaks. You could try and be a dad with a girl you'll probably resent and then that kid could have a nice, fucked up life. Or, you could do the shitty thing and just not return her calls. I hate to sound like a prick, but women are the ones who have to carry the child. The majority of the responsibility lies with them. If there was a chance casual sex would result in me carrying a burden for the rest of my life, you can bet your ass I'd be more careful, or pursue other options like abortion. but since I don't have to worry about that, I don't. And if I was in your position, I hate to say it, but I'd either make the one time payment to get the abortion, and then be really careful in the future. OR, I'd just tell her I can't do it, and let that be the end of it. But then skipping town's always a decent option in case she has homicidal friends/family who'd beat the shit out of you for being a deadbeat.
But the option you're considering can ruin all three of your lives. Chances are you will get divorced, and have to pay some sort of child support. You're gonna regret it for years to come. At least the two crappy options I mentioned above lets you cut your losses and move in with your life. But having the kid means you're in it for the long haul. PEACE.