You can go to facebook.com on your phone and the site will redirect you to the mobile version. Take note that if you use 3G, GPRS or EDGE to go to the internet, you will be charged by your Network Service if you don't have a Data Plan.
Also, if you use WiFi, it'll be free as long as your WLAN is free.
Also, you can download the Facebook Application. It's in the Download! application of your phone. Find the Download! application, refresh it, and find it there.
