The fact that you have the VIC-2FXS on the router means that you can just plug an analog phone directly into one of the FXS ports and even get a dial tone. and that is as far as you can get for now.
1. to get the 2 sites to establish voice connection you will need another FXS card on the remote router as well. with FXS cards at both locations and the right IOS image, you can then proceed to configuring the dial peers which are somewhat like static routes for voice calls. sample configurations can be found on cisco's site; here are some links http://www.cisco.com/univercd/cc/td/doc/product/access/acs_mod/1700/1750/1750voip/config.htm
http://www.cisco.com/univercd/cc/td/doc/product/rtrmgmt/cw2000/slm/1_0/uslm/practice.htm
2. to connect to the local PABX you will need a more powerful VIC card called the E&M card. And you might want to check with the vendor of the PABX for compatibility issues, and even support from them.
Finally, i will strongly recomment you don't get carried away with your discovery. VoIP can be a beast if you are not sure what you are doing. Before you suggest to your boss to go VoIP (assuming that is your intention), you might want to do some research on it. One wrong move and you will be surprised how you bandwidth will go up in smoke. In other words, VoIP implementation requires some serious planning on each leg along the way, and if you are a newbie, you might even want to consider some professional help to begin with.
I hope it was helpful.
E.
