You will need to change the settings to use the ATT SIM. I am sure you can do a search on here and find out - Main Page - BlackBerryFAQ
Here is what I have:
Options >> Advanced Options >> TCP
You will also need to have a BB dataplan to use the map features. GPS is actually free, paid for by your tax dollars, but you need a map program such as BBMaps, GoogleMaps or TeleNav to make them work.
You need the dataplan since the maps are constantly downloading map dta which cannot be stored on the BB or on the SD card.