Unusual wifi issue with iPhone 4S
I managed to solve this on my own: I gave my phone a static IP address different from the router assigned one, and everything works fine now.

I discovered that my roommate had set up a particular IP address for VPN while working from home a while back. When I got the phone and joined the network, the router assigned my phone that IP address which had various Application and Port forwarding assigned to it. Simple but took digging around in the router settings and logs.