Unusual wifi issue with iPhone 4S I've had the iPhone for less than a week. And the issue occurs while using my home WiFi network. Basically, Siri does not work, and I also have difficulty with logging in to specific sites using the app for the site (as opposed to using Safari). 

While away from home using the carrier 3G network, Siri works very well. Also, as an example, I can use my local library app for using my library account. The App Store works fine.

At home with a strong wifi signal, Siri tells me that it can't deal with my request right now and the library app continuously loads and then times out. I also have endless loading/timeout issues with the App Store.

My guess is that it's either an issue with the wireless router/modem or the iPhone itself? 

The router uses 801.11b/g. Other devices in the home (MacBook, Mac mini, a Windows machine, iPad 2, Nook Color) have no problem and perform as expected within the WiFi network. 

I have Googled and visited forums to troubleshoot this to no avail; and I'm not sure where to look next. Are there any ideas on possible router settings or iPhone settings that I need to consider at this point?

More info from a test:


  Cellular Data Off / Wireless On:
  
  
  Safari browse to various websites - OK 
  Library App - Links in the app work except for the login page.
  Siri - Always says it can't help me right now and to try again in a little while.
  
  
  Cellular Data On / Wireless Off:
  
  
  Safari browse to various websites - OK
  Library App - Works properly - OK
  Siri - Works as expected - OK
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.