Siri not working? This is a hardware problem. Bad unit.
Sorry to break this to you, but this is a hardware problem... plain and simple. We got bad units.
How do I know? I tested my wife's new 4s against my new 4s. Both are are set up identically, they are on the same account. I tested them at the same time while they were in the same place on the same wireless / 3G connection. My 4s SIRI hardly EVER works. Her 4s SIRI ALWAYS works. Never a problem. I am lucky that I have 2 new 4s phones to compare. The bad server argumet just doesn't wash. If it were a network problem NEITHER phone would work. When tested mines mostly says it can't connect to the network and hers ALWAYS works flawlessly.
Save yourself the heartach and demand a working phone from Apple. When you get one you will love it.... My wife LOVES hers... me... Not so much.
I am returning my 4s for replacement.