iPhone 3GS Sluggish All of a Sudden?

I've been happily using my 3GS since launch day, but today I started noticing that it isn't running as smoothly as it normally does.

For example: Opening up the mail up and selecting an account and then inbox. Normally everything would transition smoothly with no studders/lag, but now when I do that series of actions there is slow down and even a pause when I click on the mail I want to view.

I just did a complete restore and still having the problem.

I don't know what's going on =/

Problem solved!

Apparently when Wi-Fi is on my phone acts sluggish.

Weird.