So sorry this is happening, for awhile I thought I was just having router problems, but reset everything and both my iPad 1 and iPad 2 are recognized just fine, but no go with my Iphone 4s. Didn't realize there was a problem for while after the iOS 6 upgrade, as I don't sync to my MacBook Pro often, then other syncing problems popped up, like Kindle app won't keep things synced from or to my iPad 1 (iTunes not involved) but had worked fine before iOS 6 (Amazon isn't being at all helpful despite many posts from iPad 1 users on their forum). So today I got fed up enough with the syncing issues in general and the iPhone issue in particular, and went hunting for answers.
I honestly don't know where this solution came from, either this forum or Macrumors or another. Anyhow, I seem to have fixed the problem by turning off 3G data, leaving wifi sync checked in iTunes and then voila! My phone showed up in iTunes! So I did a wifi sync with 3G data turned off, turned 3G data back on, shut own iTunes, then I opened it again, and my phone was immediately recognized.
Lets hope it lasts. If it doesn't, I will update this post.