why my iPhone 4s doesn't have Siri?

I have the same problem.

My phone is an MC603C/A which from what I can tell is the 4s. Siri (or voice control) does appear when I hold down the home button but, when I say "text john" Siri defaults to facetime. Also, when I try to check the settings, Siri does not appear in my settings anywhere, nor does it show up in the list of restrictions. When I ask "what time is it?" the response is appropriate. Any ideas?

Nice job! Now siri is back under Settings / General after turning it back on under General / Restrictions. It does in fact disappear from the general settings when it's not turned on under restrictions. 🙂