After getting a new SIM card assigned, soft reset, hard reset, system restored, re-flashed the firmware, hours of trouble shooting w/ AT&T team, and almost purchased a third SIM Card, I finally figured out why I didn't have Data Network on my N95-3 today.
AT&T Network is definitely suffering from partial outage. At roughly 8PM, I noticed some of my applications can get access to the net, ie. OperaMini and Google Maps. Finally around 9PM, my Nokia Web Browser regains access to the web. Note, so far I've only been able to get EDGE back... not 3.5G.
I must have spent the last 10 hours sweating bullets trying to fix my phone. I can't believe with all the trouble I've gone through, its just because our data network in the NYC region has outage... What tricked me the most was that other devices were working (ie. iPhone and BlackBerry) this entire time? If they had been down, it would have helped me narrow down the problem and saved a lot of time from all the work. Now I have to go back to reinstall everything back on my phone.