I'd definitely go with a router. I used to have ISDN and I miss the hell out of it. I just moved to BFE myself, and I"m in a broadband wasteland. Can't get crap, not even ISDN.
I had a Toshiba TR-650 ISDN Router. Toshiba is out of the ISDN business now, but you can find the modems on EGay between $50 and $100. That was a great little router. Everything was set up from a Web Interface. Plus, you could configure it to allow for recieving incoming voice calls, or to constantly stay on. I also had a Cisco 805 series that worked well, but was much more complicated to set up.
That being said, I would really go for a router. If you get the Toshiba like I mentioned above, you'll be on your own to get it set up b/c Toshiba doesn't support them anymore either. But, as long as the router is "working" I guarantee you won't have any problem setting it up. It really is that simple. Plus, with this router, you're very secure as long as you don't open any ports.