Speedtest.net's testing Web app relies on Flash, so it might not work quite as well on your smartphone browser. Fortunately, if you have an Android or iOS gadget, you can grab the appropriate free Speedtest.net app and try it yourself. Some users have reported problems with the app's automatically assigning a test server located on the other side of the world--when we tried the Android app, it thought we were in Kansas instead of California. If the same kind of thing happens to you, open the Settings menu and manually choose the closest server possible. The farther away the test server is, the more network hops your data has to make to get there, which means that you'll see slower speeds and lower pings that aren't necessarily reflective of your actual network speed.
Bandwidth Testing for BlackBerry and Windows Phone 7
Not on an Android or iOS smartphone? Don't worry, you still have speed-testing options. BlackBerry users can try the Cisco Global Internet Speed Test (GIST) app, though judging from the comments in the AppWorld listing more than a few people have had problems with its either using a test server that is too far away or simply refusing to work altogether. Still, it's worth a shot.
Windows Phone 7 users, on the other hand, should grab BandWidth, a quick-and-dirty testing app. It's listed in the Marketplace simply as "BandWidth," but you can read a bit more about it in this XDA Developers thread.