Ever since the automatic upgrade to iOS 7, an iPhone that connects to my Linksys WRT54GL router running DD-WRT, slows down all other connections, from any other device. Download speed is reduced by a factor of 3 to 5, and ping times jump from 33ms to 600 - 800ms. This makes it frustratingly slow to use any web application, and appears to happen when some update is going on on the iPhone.

I only have limited access to the iPhone (it's not mine and the owner got quite annoyed with my requests to use their mobile data plan), but I have full control of the router. Banning it by its MAC isn't exactly a solution. What else can be done? I've read through some posts on Apple's board but they didn't offer a clear solution.