Q: I have an iPhone 4s on iOS 5.1.1, and whenever I'm in a conference, I tap on it, and it will not show the options to drop someone out of the call. Is this because I'm running iOS 5.1.1, or because I have an iPhone 4s

Who is your carrier? Is it a CDMA phone?

Conference calling features are more limited on CDMA phones than on GSM phones. I saw a chart recently that showed the difference in the features but I can't find it now. However, this is mentioned in the KB article:

http://support.apple.com/kb/HT4515

CDMA networks may not be able to add, swap, or merge calls in certain situations. See the iPhone User Guidefor more details.

If your carrier is Verizon, your phone is working on a CDMA network. Yes, the phone has a SIM but that's for international roaming. The phone won't work on GSM networks in the U.S.  The only way to get the conference call features would be to switch to AT&T and get an AT&T iPhone.